Forki project system check

[haacked]

Replaces and closes #192

see https://github.com/fsharp/FAKE/blob/develop/src/app/FakeLib/MSBuild/ProjectSystem.fs

This will compare all csproj files in ./Octokit/ if they have (at least) all files from ./Octokit/Octokit.csproj

[forki]

So yay it found it's first bug ;-)

[haacked]

Yep! So some folks pointed me to https://code.google.com/p/gyp/

Unfortunately that requires Ruby. I'm thinking that something F# based as part of the build might be cool. But my key requirement is that contributors should be able to use Visual Studio to add files to the "source" project Octokit.csproj in this case, and all the other project files could be generated or fixed up.

[forki]

now that we are abe to detect missing files we might add a "fix it" task.

stay tuned.