Some improvements

I tried the latest printf coloring on https://visualfsharp.codeplex.com/SourceControl/latest#tests/fsharp/core/printf/test.fsx.
It turned out coloring doesn't work reliably there because there are StackOverflow exceptions on too deep nested expressions.
This PR did a simple fix for that.

Also try to use .NET 4.5.1 assemblies to resolve Xml files more precisely.