Removed dependency on posix module; replaced posix_getpid with getmypi

Hi aran,
Please consider this pull request.
I've got rid of dependency on posix module; replaced posix_getpid with getmypid
I think this will make it easier to use with out-of-the box php installations (eg RH based linux distros) which are configured without posix by default afaik.

Cheers,
pajaco