py3: add "b" prefix to string literals related to module policy
String literals without explicit prefix in __init__.py and policy.py
are treated as unicode object on Python3, because these modules are
loaded before setup of our specific code transformation (the later
module is imported at the beginning of __init__.py).
BTW, "modulepolicy" in __init__.py is initialized by "policy.policy".
This causes issues below;
- checking "policy" value in other modules causes unintentional result
For example, "b'py' not in (u'c', u'py')" returns True
unintentionally on Python3.
- writing "policy" out fails at conversion from unicode to bytes
62939e0148f1 fixed this issue for default code path, but "policy"
can be overridden by HGMODULEPOLICY environment variable (it should
be rare case for developer using Python3, though).
This patch does:
- add "b" prefix to all string literals, which are related to module
policy, in modules above.
- check existence of HGMODULEPOLICY, and overwrite "policy" only if
it exists
For simplicity, this patch omits checking "supports_bytes_environ",
switching os.environ/os.environb, and so on (Yuya agreed this in
personal talking)