global: switch to x/sys/unix

The syscall package is locked since 1.4[1], all new changes are in x/sys[2]
The fixes for epoll/arm64 are going to be loaded to x/sys/unix. This
commit is straightforward search/replace with a couple of hand edits.

This is needed for fixing fsnotify#130

[1] https://golang.org/s/go1.4-syscall
[2] https://godoc.org/golang.org/x/sys/unix

closes fsnotify#135

Update Travis config to Go 1.5.4 and 1.6.1

Fix golint errors in windows.go for fsnotify#116

closes fsnotify#121
fixes fsnotify#116

kqueue: fix Remove-logic

`os.Lstat` does not return `error` when a file/directory exists,
so the code path  to check for newly created files after a REMOVE
on BSD was never executed.

Also, if the watched entry is a file, it has been removed from the watcher, so do a new-file-check for them as well.

This commit fixes issues on TextMate on OS X and others that uses `exchangedata` to do atomic saves.

See fsnotify#17. closes fsnotify#111.

kqueue: avoid infinite loops from symlinks cycles

The semenatics of using kqueue are already slightly different than
inotify, specifically that inotify will give you events for the symlink
itself whereas kqueue will only give events for the target of the
symlink. This preserves that behaviour, that symlinks don't get notified
on, but ensures that circular symlinks don't recurse forever.

This change pushes the resolved filename up through the stack so that
the fileExists map can be properly populated; not doing so would mean
that deleting a cyclical symlink and then replacing it with a file of
the same name would not notify for that file's creation (or subsequent
events) because we would believe that the file already existed.