Merge branch 'master' into fsharp4

Merge branch 'master' into fsharp4

Merge branch 'master' into fsharp4

Conflicts:
	src/fsharp/FSharp.Core.Unittests/FSharp.Core/PrimTypes.fs

Add "The input must be positive." error message and use it in `windowed`

Fix dotnet#266

Merge branch 'master' into fsharp4

Conflicts:
	README.md
	appveyor-build.cmd
	tests/RunTests.cmd

Merge branch 'master' into fsharp4

Merge branch 'master' into fsharp4

Merge branch 'master' into fsharp4