rebase: allow --detach when --rev is used

--rev is only a more specific --source and there is no reason to refuse to use
detach with it.

hgext/rebase.py

@@ -168,7 +168,7 b' def rebase(ui, repo, **opts):'
                 raise util.Abort(_('cannot specify both a '
                                    'revision and a source'))
             if detachf:
-                if not srcf:
+                if not (srcf or revf):
                     raise util.Abort(
                         _('detach requires a revision to be specified'))
                 if basef: