remote-bzr: fix bad state issue

Carried from remote-hg.

The problem reportedly happened after doing a push that fails, the abort
causes the state of remote-hg to go bad, this happens because
remote-hg's marks are not stored, but 'git fast-export' marks are.

Ensure that the marks are _always_ stored.

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

contrib/remote-helpers/git-remote-bzr

@@ -32,6 +32,7 @@ import os
 import json
 import re
 import StringIO
+import atexit
 
 NAME_RE = re.compile('^([^<>]+)')
 AUTHOR_RE = re.compile('^([^<>]+?)? ?<([^<>]*)>$')
@@ -728,6 +729,7 @@ def main(args):
     blob_marks = {}
     parsed_refs = {}
     files_cache = {}
+    marks = None
 
     gitdir = os.environ['GIT_DIR']
     dirname = os.path.join(gitdir, 'bzr', alias)
@@ -754,6 +756,10 @@ def main(args):
             die('unhandled command: %s' % line)
         sys.stdout.flush()
 
+def bye():
+    if not marks:
+        return
     marks.store()
 
+atexit.register(bye)
 sys.exit(main(sys.argv))