Summary: Workspaces are most useful to test different versions (commits) of
the tree within the same repository, but in many cases you want to check out a
specific commit within a workspace.
Make that trivial with a `--revision` option which will be used as the basis
for the new workspace. If no `-r` option is given, then the previous behavior
applies: the workspace is created with a working copy commit created on top of
the current working copy commit's parent.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I23549efe29bc23fb9f75437b6023c237