AttributeError is raiesd by hdfdump=1 parameter

[Jun Omae]

This issue is introduced in [14186] (#12131).

2015-08-05 16:59:05,888 Trac[main] ERROR: Internal Server Error:
Traceback (most recent call last):
  File "/venv/trac/1.0.8/lib/python2.5/site-packages/trac/web/main.py", line 551, in _dispatch_request
    dispatcher.dispatch(req)
  File "/venv/trac/1.0.8/lib/python2.5/site-packages/trac/web/main.py", line 258, in dispatch
    out = StringIO.StringIO()
AttributeError: class StringIO has no attribute 'StringIO'

trac/web/main.py

@@ -27 +27 @@
 from pprint import pformat, pprint
 import re
 import sys
-import StringIO
 
 from genshi.builder import tag
 from genshi.output import DocType
@@ -255 +254 @@
                     if 'hdfdump' in req.args:
                         req.perm.require('TRAC_ADMIN')
                         # debugging helper - no need to render first
-                        out = StringIO.StringIO()
+                        out = StringIO()
                         pprint(data, out)
                         req.send(out.getvalue(), 'text/plain')