New Feature: replace captcha library with open source library. Adds audio support to captcha for accessibility [requires flash on client]

Ported from master-2.x branch

Resolves (Part or all) of bugs:

#0010972: openbase_dir breaks captcha generation
#0008796: The letters in the catchpa on account creation page are too small
#0010976: Remove instances of pass-by-reference (deprecated in PHP 5.3.0)
#0010028: Registrations by bots via captcha exploit
#0008462: Captcha will benefit supporting other than jpeg format
#0008129: Alternative to captchas
Remove legacy references to wingraphviz module that was removed several years ago
Sync in another batch of db_prepare_int/numrows/phpdoc stuff
Remove check for really old pre 1.x installer logic