remote-hg: add option to not track branches

Some people prefer it this way.

 % git config --global remote-hg.track-branches false

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>

contrib/remote-helpers/git-remote-hg

@@ -449,22 +449,22 @@ def list_head(repo, cur):
     g_head = (head, node)
 
 def do_list(parser):
-    global branches, bmarks, mode
+    global branches, bmarks, mode, track_branches
 
     repo = parser.repo
-    for branch in repo.branchmap():
-        heads = repo.branchheads(branch)
-        if len(heads):
-            branches[branch] = heads
-
     for bmark, node in bookmarks.listbookmarks(repo).iteritems():
         bmarks[bmark] = repo[node]
 
     cur = repo.dirstate.branch()
 
     list_head(repo, cur)
 
-    if mode != 'hg':
+    if track_branches:
+        for branch in repo.branchmap():
+            heads = repo.branchheads(branch)
+            if len(heads):
+                branches[branch] = heads
+
         for branch in branches:
             print "? refs/heads/branches/%s" % branch
 
@@ -713,16 +713,22 @@ def main(args):
     global prefix, dirname, branches, bmarks
     global marks, blob_marks, parsed_refs
     global peer, mode, bad_mail, bad_name
+    global track_branches
 
     alias = args[1]
     url = args[2]
     peer = None
 
-    cmd = ['git', 'config', '--get', 'remote-hg.hg-git-compat']
     hg_git_compat = False
+    track_branches = True
     try:
+        cmd = ['git', 'config', '--get', 'remote-hg.hg-git-compat']
         if subprocess.check_output(cmd) == 'true\n':
             hg_git_compat = True
+            track_branches = False
+        cmd = ['git', 'config', '--get', 'remote-hg.track-branches']
+        if subprocess.check_output(cmd) == 'false\n':
+            track_branches = False
     except subprocess.CalledProcessError:
         pass