cleanup referenceresolution.fs/fsi

ReferenceResolution.fs/fsi has long been messy in a way that obscured what
it does. This is some code cleanup (no change in functionality) to remove
some of the obscurity. This came from reviewing the code with Robin Neatherway.

closes http://visualfsharp.codeplex.com/SourceControl/network/forks/dsyme/cleanup/contribution/7671

commit dbd480e5f58418782bcc0f0dde54a5bc8bfe346f
Author: Don Syme <[email protected]>
Date:   Mon Nov 10 16:21:12 2014 +0000

    put net10 and net11 back

commit ac83e77a8d6a9fe93dab5afa904761feec27be08
Author: Don Syme <[email protected]>
Date:   Mon Nov 10 16:05:52 2014 +0000

    cleanup ReferenceResolution.fs

Author: dsyme

src/fsharp/CompileOps.fs

@@ -2634,7 +2634,7 @@ type TcConfig private (data : TcConfigBuilder,validate:bool) =
                     | MSBuildResolver.RuntimeLike ->
                         [System.Runtime.InteropServices.RuntimeEnvironment.GetRuntimeDirectory()] 
                     | _ -> 
-                        let frameworkRoot = MSBuildResolver.DotNetFrameworkReferenceAssembliesRootDirectory
+                        let frameworkRoot = MSBuildResolver.DotNetFrameworkReferenceAssembliesRootDirectoryOnWindows
                         let frameworkRootVersion = Path.Combine(frameworkRoot,tcConfig.targetFrameworkVersionMajorMinor)
                         [frameworkRootVersion]
                 with e ->