set the MACOSX_DEPLOYMENT_TARGET env variable for the interpreter process
on OS X.  This could cause failures in non-distutils subprocesses and was
unreliable since tests or user programs could modify the interpreter
environment after distutils set it.  Instead, have distutils set the
the deployment target only in the environment of each build subprocess.

Continue to use the previous algorithm for deriving the deployment target
value:
    if MACOSX_DEPLOYMENT_TARGET is not set in the interpreter's env:
        use the interpreter build configure MACOSX_DEPLOYMENT_TARGET
    elif the MACOSX_DEPLOYMENT_TARGET env value >= configure value:
        use the env MACOSX_DEPLOYMENT_TARGET
    else: # env value less than interpreter build configure value
        raise exception
This allows building extensions that can only run on newer versions of
the OS than the version python was built for, for example with a python
built for 10.3 or later and an extension that needs to be built for 10.5.

test_build_ext.

test_build_ext of test_distutils is no longer silently skipped when
run outside of a build directory.

os.lchflags() are once again built on systems that support these
functions (*BSD and OS X).  Also add new stat file flags for OS X
(UF_HIDDEN and UF_COMPRESSED).  Also add additional tests for
os.chflags() and os.lchflags(). (Tests by Garrett Cooper)

on Mac OS X.  (Patch by Ronald Oussoren)

A patch from Vincent Legoll.

Patch by Akira Kitada.

Patch by Francisco Martín Brugué.

The new wording is based on the comments in the code, which
match the actual behavior.

Locks are implemented using a mutex and a condition variable of the pthread
library on FreeBSD6. POSIX condition variables cannot be interrupted by signals
(see pthread_cond_wait manual page).

Cannot test an empty environment on Windows: Windows requires at least the
SYSTEMROOT environment variable to start Python.

Mac OS X adds __CF_USER_TEXT_ENCODING variable to an empty environment. Fix
also the test on the Py_ENABLE_SHARED config varible: test that the variable is
present, don't check it's value.

Try also to get more informations about the Mac OS X failure: display the keys
of the environment, instead of just the number of variables.