Xdebug (A PHP extension for debugging PHP scripts)

The Xdebug extension helps you debugging your script by providing a lot of 
valuable debug information.  The debug information that Xdebug can provide 
includes the following: stack traces and function traces in error messages, 
memory allocation and protection for infinite recursions. Xdebug also 
provides profiling information for PHP, scripts, code coverage analysis and 
capabilities to debug PHP scripts interactively with a debug client.

This requires libedit.

Once you install xdebug, add the following line to php.ini:
	zend_extension = "/usr/lib/php/extensions/xdebug.so"

Restart your webserver if you're using php with it, and as a recomendation 
from xdebug's README:   "Write a PHP page that calls "phpinfo();" Load it 
in a browser and look for the info on the xdebug module.  If you see it, 
you have been successful!"