convert: add default constructor for converter_sink

hgext/convert/common.py

@@ -117,7 +117,8 b' class converter_sink(object):'
     def __init__(self, ui, path):
         """Initialize conversion sink (or raise NoRepo("message")
         exception if path is not a valid repository)"""
-        raise NotImplementedError()
+        self.path = path
+        self.ui = ui
 
     def getheads(self):
         """Return a list of this repository's heads"""

hgext/convert/hg.py

@@ -16,8 +16,7 b' from common import NoRepo, commit, conve'
 
 class mercurial_sink(converter_sink):
     def __init__(self, ui, path):
-        self.path = path
-        self.ui = ui
+        converter_sink.__init__(self, ui, path)
         self.branchnames = ui.configbool('convert', 'hg.usebranchnames', True)
         self.clonebranches = ui.configbool('convert', 'hg.clonebranches', False)
         self.tagsbranch = ui.config('convert', 'hg.tagsbranch', 'default')