I was brave and just tried out the new Shelve functionality... seems to
work well, but I didn't realise that when you unshelve it will unshelve
into the active changelist, rather than use or reconstitute the old
one... so my files got a bit mixed up...
To prevent this problem, I think when Unshelve is executed the user
should be asked to choose or create the changelist to unshelve into.