remote-bzr: iterate revisions properly

This way we don't need to store the list of all the revisions, which
doesn't seem to be very memory efficient with bazaar's design, for
whatever reason.

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

contrib/remote-helpers/git-remote-bzr

@@ -286,9 +286,10 @@ def export_branch(repo, name):
     last_revno, _ = branch.last_revision_info()
     total = last_revno - tip_revno
 
-    revs = [revid, seq for revid, _, seq, _ in revs if not marks.is_marked(revid)]
+    for revid, _, seq, _ in revs:
 
-    for revid, seq in revs:
+        if marks.is_marked(revid):
+            continue
 
         rev = repo.get_revision(revid)
         revno = seq[0]