events api improvement and joomla event listing bug fix

the joomla menu items listing of available events does not pull the list of current events properly. the issue stems from an inability to pull current/future events from the API, and the max_results limitation for that API (we can't pull "all" events and then filter by current/future). see: http://forum.civicrm.org/index.php?topic=17081

i propose we extend the events search api to allow for another special parameter – isCurrent – that will retrieve only current and future events.

the attached patches extend the events api, and fix the joomla menu listing issue – dependent on the API fix. there are other minor fixes to the joomla event listing.

if the events api improvement is not accepted, let me know as I'll develop a workaround for the joomla events listing so we can get it patched in the next revision if at all possible