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.