pycompat: add util.stringio to handle py3 divergence

util.stringio = cStringIO.StringIO / io.StringIO

mercurial/pycompat.py

@@ -11,6 +11,13 b' This contains aliases to hide python ver'
 from __future__ import absolute_import
 
 try:
+    import cStringIO as io
+    stringio = io.StringIO
+except ImportError:
+    import io
+    stringio = io.StringIO
+
+try:
     import Queue as _queue
     _queue.Queue
 except ImportError:

mercurial/util.py

@@ -49,6 +49,7 b' from . import ('
 for attr in (
     'empty',
     'queue',
+    'stringio',
 ):
     globals()[attr] = getattr(pycompat, attr)