Replaced xcopy with robocopy

xcopy [doesn't handle paths longer than 254 characters](http://www.terminally-incoherent.com/blog/2007/02/05/xcopy-insufficient-memory/) and it's recommended to use [robocopy](http://technet.microsoft.com/en-us/library/cc733145.aspx) (available on Windows 7, Windows 8, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012) instead.