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.

variables, start with an empty environment.

processes if negative or null.