Try to make FAKE work with the F# 3.1 compiler

- [x] Compile F# 3.1 on windows
- [x] Make it accept the FSharp.Core 4.3.1.0
- [x] Make FAKE build working (see http://teamcity.codebetter.com/viewType.html?buildTypeId=bt1144)
- [ ] Make FAKE building itself using FAKE + F# 3.1 (inception style)