PHP Limits: Make them configurable

In cron.php, it sets PHP maximum execution time to 240 secs which is only 4 minutes. Since it invokes cron jobs that user-provided modules may have, we shouldn't have placed that hard-wired limit. It's possible that someone may need to perform long operations via PHP (the longest php script I ever executed took many hours to complete).

I suppose to make maximum execution time and maximum allowed memory utilisation settings configurable in settings.php, both of these settings can be changed on-the-fly while a script is running, so you would place a variable instead of a hardwired number in the relevant functions.

With these settings a script can run forever:

ini_set( 'memory_limit', -1 );

set_time_limit(0);

The configurable code would look like this:

ini_set( 'memory_limit', $a );

set_time_limit($b);

The user would specify $a and $b in their settings file(s). Drupal should be able to assume some default values for these variables if they aren't set. So there could be some is_set() test or something similar before their use.