At Victor's suggestion, I've added a file called core_php_API.php
This file has a new function to check a version string against the
current version (called php_version_at_least() ) which we can use to
check for features or whatnot.
All compatibility code (like definition of DIRECTORY_SEPARATOR,
simulation of register_globals, etc) that I'm aware of has been moved
into this file and any new code should go there.
This file is included very first in core_API.php so that all the other
included files can benefit from it.
We also added a check to make sure that the php version is greater that
4.0.3 (our minimum requirement) and print an error message and die if is
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