Added support for unshelve command to unshelve into a TFS Branch.

We needed to be able to unshelve to a TFS branch pulled into GIT for our code reviews.  The original form of the unshelve command always went to the trunk (default id).  I added a command line parameter so you can direct the shelf set to the appropriate branch in GIT.  Once that was in, the remaining code worked perfectly.

I updated that command and the Docs to go with it.