Added portable support for FSharp.Core

Although I have included Profile88 in the import and PropertyGroup
section it wont build on mono as this profile is not supported.

Only profiles 5,6,14,19,24,37,42,47,136,147,158 for .Net 4.0 and
7,49,78 for .Net 4.5

Conflicts:
	src/FSharpSource.targets
Added parenthesis around OR clause to make the condition logic clear.
Added parenthesis to make condition logic clear.
Merge pull request #239 from 7sharp9/master

Added portable support for FSharp.Core