Add branch_name_in_commit plugin

plugins/branch_name_in_commit/README.md

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+## Branch Name in Commit Message
+
+Mercurial has a much stronger notion of branches than Git,
+and some parties may not wish to lose the branch information
+during the migration to Git. You can use this plugin to either
+prepend or append the branch name from the mercurial
+commit into the commit message in Git.
+
+To use the plugin, add
+`--plugin branch_name_in_commit=(start|end)`.

plugins/branch_name_in_commit/__init__.py

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+def build_filter(args):
+    return Filter(args)
+
+class Filter:
+    def __init__(self, args):
+        if not args in ['start','end']:
+            raise Exception('Cannot have branch name anywhere but start and end')
+        self.pos = args
+
+    def commit_message_filter(self,commit_data):
+        if self.pos == 'start':
+            commit_data['desc'] = commit_data['branch'] + '\n' + commit_data['desc']
+        if self.pos == 'end':
+            commit_data['desc'] = commit_data['desc'] + '\n' + commit_data['branch']