All code (util.byte_compile, build_py, install_lib) can now create .pyc
and/or.pyo files according to options given by users, without
interference from the calling Python?s own optimize mode or from the
sys.dont_write_bytecode switch.

The rationale is that packaging gives control over the creation of
.pyc/.pyo files to the user with its own explicit option, and the
behavior should not be changed if the calling Python happens to run with
-B or -O for whatever reason.

This is actually a bug fix, not an improvement: Digging into the early
history of distutils shows that the original author wanted this behavior
(see for example comments in build_py in r12940).

Backports:
- sysconfig is now always imported from our backports
- when hashlib is not found, our backport is used instead of the md5
  module (debatable; we could just drop hashlib)

Version-dependent features:
- PEP 370 features are only enabled for 2.6+
- the check for sys.dont_write_bytecode was fixed to use getattr
  with a default value instead of hasattr

Idioms/syntax:
- octal literals lost their extra 0
- misused try/except blocks have been changed back to try/finally
  (it?s legal in 2.4 too, it?s only try/except/finally that isn?t)
- exception catching uses the regular 2.x idiom instead of sys.exc_info
- file objects are closed within finally blocks (this causes much
  whitespace changes but actually makes diff with packaging easier)

Renamed modules:
- some missed renamings (_thread, Queue, isAlive, urllib.urlsplit, etc.)
  were fixed

Other:
- a few false positive replacements of ?packaging? by ?distutils2? in
  comments or docstrings were reverted
- util.is_packaging regained its name
- assorted whitespace/comment/import changes to match packaging

collision with the distutils2 installer (working with dependencies).