mq: wrap qimport phase movement in a transaction

Phases are not yet inside the transaction, but we need to prepare for it. So we
wrap the phase movement inside a transaction.

hgext/mq.py

@@ -1975,16 +1975,21 class queue(object):
                 lastparent = None
 
             diffopts = self.diffopts({'git': git})
+            tr = repo.transaction('qimport')
+            try:
             for r in rev:
                 if not repo[r].mutable():
                     raise util.Abort(_('revision %d is not mutable') % r,
-                                     hint=_('see "hg help phases" for details'))
+                                         hint=_('see "hg help phases" '
+                                                'for details'))
                 p1, p2 = repo.changelog.parentrevs(r)
                 n = repo.changelog.node(r)
                 if p2 != nullrev:
-                    raise util.Abort(_('cannot import merge revision %d') % r)
+                        raise util.Abort(_('cannot import merge revision %d')
+                                         % r)
                 if lastparent and lastparent != r:
-                    raise util.Abort(_('revision %d is not the parent of %d')
+                        raise util.Abort(_('revision %d is not the parent of '
+                                           '%d')
                                      % (r, lastparent))
                 lastparent = p1
 
@@ -2010,6 +2015,9 class queue(object):
                 self.parseseries()
                 self.applieddirty = True
                 self.seriesdirty = True
+                tr.close()
+            finally:
+                tr.release()
 
         for i, filename in enumerate(files):
             if existing: