add vfs snapshot capability for future tests
add vfs snapshot capability for future tests

Microsoft/TypeScript,kpreisser/TypeScript,alexeagle/TypeScript,Microsoft/TypeScript,donaldpipowitch/TypeScript,Microsoft/TypeScript,SaschaNaz/TypeScript,microsoft/TypeScript,nojvek/TypeScript,nojvek/TypeScript,minestarks/TypeScript,minestarks/TypeScript,SaschaNaz/TypeScript,basarat/TypeScript,microsoft/TypeScript,nojvek/TypeScript,basarat/TypeScript,kitsonk/TypeScript,donaldpipowitch/TypeScript,RyanCavanaugh/TypeScript,weswigham/TypeScript,kitsonk/TypeScript,basarat/TypeScript,RyanCavanaugh/TypeScript,donaldpipowitch/TypeScript,alexeagle/TypeScript,minestarks/TypeScript,nojvek/TypeScript,kitsonk/TypeScript,SaschaNaz/TypeScript,weswigham/TypeScript,donaldpipowitch/TypeScript,kpreisser/TypeScript,RyanCavanaugh/TypeScript,SaschaNaz/TypeScript,alexeagle/TypeScript,kpreisser/TypeScript,weswigham/TypeScript,basarat/TypeScript,microsoft/TypeScript