Update head2branch plugin to accept hg commit hash

The revision number isn't a unique identifier of commits across
repository clones and forks, while the hg hash is guaranteed to be stable.

plugins/head2branch/README.md

@@ -2,11 +2,12 @@
 
 `fast-export` can only handle one head per branch. This plugin makes it possible
 to create a new branch from a head by specifying the new branch name and
-the first divergent commit for that head.  The revision number for the commit
-should be in decimal form.
+the first divergent commit for that head.
+
+Note: the hg hash must be in the full form, 40 hexadecimal characters.
 
 Note: you must run `fast-export` with `--ignore-unnamed-heads` option,
 otherwise, the conversion will fail.
 
-To use the plugin, add the command line flag `--plugin head2branch=name,<rev>`.
+To use the plugin, add the command line flag `--plugin head2branch=name,<hg_hash>`.
 The flag can be given multiple times to name more than one head.

plugins/head2branch/__init__.py

@@ -7,17 +7,18 @@ class Filter:
 
     def __init__(self, args):
         args = args.split(',')
-        self.branch_name = args[0]
-        self.starting_commit = int(args[1])
+        self.branch_name = args[0].encode('ascii', 'replace')
+        self.starting_commit_hash = args[1].encode('ascii', 'strict')
         self.branch_parents = set()
 
     def commit_message_filter(self, commit_data):
+        hg_hash = commit_data['hg_hash']
         rev = commit_data['revision']
         rev_parents = commit_data['parents']
-        if (rev == self.starting_commit
+        if (hg_hash == self.starting_commit_hash
             or any(rp in self.branch_parents for rp in rev_parents)
             ):
             self.branch_parents.add(rev)
-            commit_data['branch'] = self.branch_name.encode('ascii', 'replace')
+            commit_data['branch'] = self.branch_name
             sys.stderr.write('\nchanging r%s to branch %r\n' % (rev, self.branch_name))
             sys.stderr.flush()