convert: honor 2.3 compatibility (rsplit)

hgext/convert/subversion.py

@@ -463,7 +463,7 b' class svn_source(converter_source):'
         return int(rev.split('@')[-1])
 
     def revsplit(self, rev):
-        url, revnum = rev.encode(self.encoding).rsplit('@', 1)
+        url, revnum = strutil.rsplit(rev.encode(self.encoding), '@', 1)
         revnum = int(revnum)
         parts = url.split('/', 1)
         uuid = parts.pop(0)[4:]