Add more Gen extension methods.
Add more Gen extension methods.

fscheck/FsCheck,cloudRoutine/FsCheck,jhamm/FsCheck,cloudRoutine/FsCheck,paulyoung/FsCheck,forki/FsCheck,forki/FsCheck,fscheck/FsCheck,fsharp/FsCheck,sideeffffect/FsCheck,ploeh/FsCheck,ErikSchierboom/FsCheck,paulyoung/FsCheck