tests/test-issue436

py3kcompat: added a "compatibility layer" for py3k

This patch adds some ugly constructs. The first of them is bytesformatter, a
function that formats strings like when '%' is called. The main motivation for
this function is py3k's strange behavior:

>>> 'foo %s' % b'bar'
"foo b'bar'"
>>> b'foo %s' % b'bar'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for %: 'bytes' and 'bytes'
>>> b'foo %s' % 'bar'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for %: 'bytes' and 'str'

In other words, if we can't format bytes with bytes, and recall that all
mercurial strings will be converted by a fixer, then things will break badly if
we don't take a similar approach.

The other addition with this patch is that the os.environ dictionary is
monkeypatched to have bytes items. Hopefully this won't be needed in the
future, as python 3.2 might get a os.environb dictionary that holds bytes
items.

#!/bin/sh

hg init a
cd a
hg -v log -v
hg -v log -v x
true