Project cache invalidating

It does not work yet. The following exception is raised after renaming a file:

```
There are 1 error(s).
[Language Service] System.Exception: Could not find requested input '(startup (1,0--1,80) IsSynthetic=false, "L:\git\Library3\Library1.fs", false)' named 'FileNames' in set [(0, Available('(startup (1,0--1,80) IsSynthetic=false, L:\git\Library3\Library11.fs, False)' as of 26.02.2014 22:45:36)); (1, Available('(startup (1,0--1,80) IsSynthetic=false, L:\git\Library3\File51.fs, True)' as of 26.02.2014 22:45:36))]
   at Microsoft.FSharp.Compiler.IncrementalBuild.GetSlotByInput[T](String name, T input, PartialBuild build, FSharpFunc`2 equals)
   at Microsoft.FSharp.Compiler.IncrementalFSharpBuild.IncrementalBuilder.GetSlotOfFileName(String filename)
   at Microsoft.FSharp.Compiler.IncrementalFSharpBuild.IncrementalBuilder.GetParseResultsForFile(String filename)
   at <StartupCode$FSharp-Compiler-Service>.$Service.GetBackgroundCheckResultsForFileInProject@1943.Invoke(Unit unitVar0)
   at Microsoft.FSharp.Compiler.SourceCodeServices.Reactor.RunAsyncOp@248.Invoke(Unit unitVar0) exception occurs while updating.
```