Added caDebug function.

This is inspired by Drupal's debug(). The idea is to have a simple and
unified way to print debugging information that can be turned off
globally by default for releases and on production systems. It also
looks a bit nicer than a plain old print_r() or var_dump().
Oops. Well there you go: I left a debug statement in that I didn't notice because debugging was disabled :-)
Merge pull request #21 from collectiveaccess/debug

New unified debugging function