convert: manually set encoding to UTF-8

Right now the backends assume we're working in UTF-8 and there's
no good way to ignore the encoding when adding revisions.

hgext/convert/__init__.py

@@ -269,6 +269,8 b' def _convert(ui, src, dest=None, mapfile'
     srcauthor=whatever string you want
     '''
 
+    util._encoding = 'UTF-8'
+
     srcc = converter(ui, src)
     if not hasattr(srcc, "getcommit"):
         raise util.Abort("%s: can't read from this repo type" % src)