bundle2: make sure standard stream are binary

Python on Windows apparently use encoded stream by default. We use the same
trick than elsewhere in the code to make them binary.

This should fix the current buildbot failure on windows.

tests/test-bundle2.t

@@ -8,6 +8,14 b' Create an extension to test bundle2 API'
   > code. We still need to be able to test it while it grow up.
   > """
   > 
+  > try:
+  >     import msvcrt
+  >     msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
+  >     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
+  >     msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
+  > except ImportError:
+  >     pass
+  > 
   > import sys
   > from mercurial import cmdutil
   > from mercurial import util