Clone performance slightly improved
Merge remote-tracking branch 'origin/master' into p518

Conflicts:
	GitTfs/Core/TfsChangeset.cs

Other merge fixes:
	GitTfs/Core/GitObject.cs
	GitTfs/Util/ChangeSieve.cs
	GitTfsTest/Core/ChangeSieveTest.cs
Merge pull request #518 from KindDragon/clone-performance

Clone performance slightly improved.