r62555 has the unfortunate effect that source lines are no more indented
in tracebacks, as in:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\python\trunk\lib\re.py", line 150, in sub
return _compile(pattern, 0).sub(repl, string, count)
  File "C:\python\trunk\lib\re.py", line 276, in filter
return sre_parse.expand_template(template, match)
  File "c:\python\trunk\lib\sre_parse.py", line 793, in expand_template
raise error, "unmatched group"
sre_constants.error: unmatched group

And IMO, test_traceback.test_traceback_indentation() tests the wrong
behaviour :-(
I join a tentative patch to correct the problem.