Attached is modified version including nesting and custom title support

Attached is a modified version of the module for Drupal 6 that incorporates the D6 porting by sze and adds two new features:

1) Nesting. The regexp function is rewritten based on the recursive BB code example from http://uk.php.net/manual/en/function.preg-replace-callback.php (example #3).
This allows collapsible boxes to placed inside each other.

2) Custom title. Allows for an optional title="my custom title" parameter in opening tag, ie [collapse title="My custom title"] or [collapse collapsed title="My custom title"]. I find this useful because I like to name the collapsible sections without having a header inside. The title must be after the "collapsible" option if used.

This should be backwards compatible with previous versions of the module.

Please note that I have not fully tested it, but it does work on my site. I hope it is useful to people.
Pukku, if you like the additions please add them to an official release!

Regards,
Justyn.