convert/gnuarch: keep track of original revision in extra headers

It seems to be standard to populate the .rev attribute of a commit
to keep track of original SCM revision names.

Just do it(tm).

hgext/convert/gnuarch.py

@@ -141,7 +141,7 b' class gnuarch_source(converter_source, c'
     def getcommit(self, rev):
         changes = self.changes[rev]
         return commit(author = changes.author, date = changes.date,
-                      desc = changes.summary, parents = self.parents[rev])
+                      desc = changes.summary, parents = self.parents[rev], rev=rev)
 
     def gettags(self):
         return self.tags