Added support for compiling against .NET 4.5
Removed comments from last commit (should have been removed then, was only for testing).
IronPython compiling agains v4.5

Pull #85
"Everything" compiles
Renamed to FEATURE_
Merge remote-tracking branch 'Alxandr/Net45'
Update IronPython.sln with the v45{Debug,Release} targets.