Version resolver should handle pinned down versions in libraries

##### Issue description

As described in the [docs](https://docs.pipenv.org/advanced/#pipfile-vs-setup-py) it is expected that libraries do not pin dependencies to specific versions. However this restriction is many times ignored or simply not seen in projects. I, as a user, should be able to pin down a dependency in my library to a version if that is the only version the given package works with.

As a subsequent behavior, if my application uses the same dependency as one of the libs I use, performing `pipenv install` or `pipenv update` simply fails if I do not pin down dependency to the same version as my library uses. This requires pinning dependencies in the Pipfile without any particular reason on my side (also consider updates of libs that can cause pinned versions to be rotten).

##### Expected result

Dependency resolver is smart enough to resolve dependencies even though libraries I'm using have pinned down versions.

##### Actual result

If I use the same library as one of my dependencies, `pipenv install` or `pipenv update` fails:

<details>
  <summary>Standard error</summary>

```
Creating a virtualenv for this project...
Pipfile: /tmp/tmpqc1yuhsw/Pipfile
Using /usr/bin/python3.6m (3.6.5) to create virtualenv...
Running virtualenv with interpreter /usr/bin/python3.6m
Using base prefix '/usr'
New python executable in /tmp/tmpqc1yuhsw/.venv/bin/python3.6m
Also creating executable in /tmp/tmpqc1yuhsw/.venv/bin/python
Installing setuptools, pip, wheel...done.

Virtualenv location: /tmp/tmpqc1yuhsw/.venv
Locking [dev-packages] dependencies...
Locking [packages] dependencies...

Warning: Your dependencies could not be resolved. You likely have a mismatch in your sub-dependencies.
  You can use $ pipenv install --skip-lock to bypass this mechanism, then run $ pipenv graph to inspect the situation.
  Hint: try $ pipenv lock --pre if it is a pre-release dependency.
Could not find a version that matches pyyaml==3.12,==4.2b4 (from -r /tmp/pipenv-130k553c-requirements/pipenv-86747my2-constraints.txt (line 7))
Tried: 3.10, 3.10, 3.11, 3.11, 3.12, 3.12, 3.12, 3.12, 3.12, 3.12, 3.12, 3.12, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13, 3.13
Skipped pre-versions: 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13b1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 3.13rc1, 4.2b1, 4.2b2, 4.2b4, 4.2b4, 4.2b4, 4.2b4, 4.2b4
There are incompatible versions in the resolved dependencies.


```

</details>

Relevant parts of the dependency graph:

<details>
  <summary>Dependency graph</summary>

```
aiogremlin [required: ==3.2.6rc1, installed: 3.2.6rc1]
   ...
    - PyYAML [required: ==3.12, installed: 4.2b4]
...
PyYAML [required: Any, installed: 4.2b4]
...
```

</details>

See this automated report for real world example - https://github.com/thoth-station/package-releases-job/issues/47

##### Steps to replicate

```pipenv install aiogremlin==3.2.6rc1 pyyaml --pre```

-------------------------------------------------------------------------------

<details><summary>$ pipenv --support</summary>

Pipenv version: `'2018.7.1'`

Pipenv location: `'/usr/local/lib/python3.6/site-packages/pipenv'`

Python location: `'/usr/bin/python3'`

Other Python installations in `PATH`:

  - `2.7`: `/usr/bin/python2.7`
  - `2.7`: `/usr/bin/python2.7`
  - `3.6`: `/usr/bin/python3.6m`
  - `3.6`: `/usr/bin/python3.6`

  - `2.7.15`: `/usr/bin/python`
  - `2.7.15`: `/usr/bin/python2`
  - `3.6.5`: `/usr/bin/python3`

PEP 508 Information:

```
{'implementation_name': 'cpython',
 'implementation_version': '3.6.5',
 'os_name': 'posix',
 'platform_machine': 'x86_64',
 'platform_python_implementation': 'CPython',
 'platform_release': '4.17.3-200.fc28.x86_64',
 'platform_system': 'Linux',
 'platform_version': '#1 SMP Tue Jun 26 14:17:07 UTC 2018',
 'python_full_version': '3.6.5',
 'python_version': '3.6',
 'sys_platform': 'linux'}
```

System environment variables:

  - `XDG_SEAT`
  - `GIO_LAUNCHED_DESKTOP_FILE_PID`
  - `XDG_SESSION_ID`
  - `WINDOWPATH`
  - `DISPLAY`
  - `BASH_ENV`
  - `HOSTNAME`
  - `COLORTERM`
  - `QTLIB`
  - `ENV`
  - `GNOME_DESKTOP_SESSION_ID`
  - `LOGNAME`
  - `MODULESHOME`
  - `GUESTFISH_PS1`
  - `SHELL`
  - `FPATH`
  - `GUESTFISH_INIT`
  - `PATH`
  - `HISTCONTROL`
  - `XMODIFIERS`
  - `GIO_LAUNCHED_DESKTOP_FILE`
  - `SSH_AUTH_SOCK`
  - `GUESTFISH_OUTPUT`
  - `XAUTHORITY`
  - `XDG_SESSION_DESKTOP`
  - `GDMSESSION`
  - `QT_IM_MODULE`
  - `HISTSIZE`
  - `SSH_ASKPASS`
  - `LESSOPEN`
  - `OLDPWD`
  - `XDG_MENU_PREFIX`
  - `MODULES_RUN_QUARANTINE`
  - `MAIL`
  - `USERNAME`
  - `XDG_RUNTIME_DIR`
  - `MODULES_CMD`
  - `MODULEPATH`
  - `DESKTOP_SESSION`
  - `GUESTFISH_RESTORE`
  - `QTDIR`
  - `USER`
  - `PWD`
  - `TERMINATOR_UUID`
  - `VTE_VERSION`
  - `QTINC`
  - `TERMINATOR_DBUS_PATH`
  - `HOME`
  - `DESKTOP_AUTOSTART_ID`
  - `XDG_DATA_DIRS`
  - `LOADEDMODULES`
  - `MODULEPATH_modshare`
  - `LANG`
  - `SHLVL`
  - `XDG_VTNR`
  - `GDM_LANG`
  - `TERMINATOR_DBUS_NAME`
  - `XDG_SESSION_TYPE`
  - `DBUS_SESSION_BUS_ADDRESS`
  - `XDG_CURRENT_DESKTOP`
  - `TERM`
  - `SESSION_MANAGER`
  - `LS_COLORS`
  - `ZSH`
  - `PAGER`
  - `LESS`
  - `LSCOLORS`
  - `VIRTUALENVWRAPPER_PROJECT_FILENAME`
  - `VIRTUALENVWRAPPER_WORKON_CD`
  - `VIRTUALENVWRAPPER_SCRIPT`
  - `WORKON_HOME`
  - `VIRTUALENVWRAPPER_HOOK_DIR`
  - `LC_CTYPE`
  - `GOPATH`
  - `_`
  - `PYTHONDONTWRITEBYTECODE`
  - `PIP_PYTHON_PATH`

Pipenv–specific environment variables:


Debug–specific environment variables:

  - `PATH`: `/home/fpokorny/bin:/usr/local/cuda-8.0/bin:/usr/local/bin:/usr/lib64/qt-3.3/bin:/usr/share/Modules/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/home/fpokorny/bin`
  - `SHELL`: `/usr/bin/zsh`
  - `LANG`: `en_US.UTF-8`
  - `PWD`: `/tmp/a`


---------------------------

Contents of `Pipfile` ('/tmp/a/Pipfile'):

```toml
[[source]]
url = "https://pypi.org/simple"
verify_ssl = true
name = "pypi"

[packages]
aiogremlin = "==3.2.6rc1"
pyyaml = "*"

[dev-packages]

[requires]
python_version = "3.6"

[pipenv]
allow_prereleases = true

```

</details>


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Version resolver should handle pinned down versions in libraries #2589

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