remote-bzr: use proper push method

Do not just randomly synchronize the revisions with no checks at
all.

I don't have any evidence that there's anything wrong with the
current code, which Bazaar seems to use, but for different purposes.
Let's use the logic Bazaar UI uses to avoid surprises.

Also, add a non-ff check.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Felipe Contreras

contrib/remote-helpers/git-remote-bzr

@@ -630,12 +630,12 @@ def do_export(parser):
     for ref, revid in parsed_refs.iteritems():
         if ref == 'refs/heads/master':
             repo.generate_revision_history(revid, marks.get_tip('master'))
-            revno, revid = repo.last_revision_info()
             if peer:
-                if hasattr(peer, "import_last_revision_info_and_tags"):
-                    peer.import_last_revision_info_and_tags(repo, revno, revid)
-                else:
-                    peer.import_last_revision_info(repo.repository, revno, revid)
+                try:
+                    repo.push(peer, stop_revision=revid)
+                except bzrlib.errors.DivergedBranches:
+                    print "error %s non-fast forward" % ref
+                    continue
             else:
                 wt = repo.bzrdir.open_workingtree()
                 wt.update()