BuddyPress 1.6 Fixes and Warning Removal

BuddyPress 1.6 begins the move away from using the $bp global. I've gone through and replaced the feed checks with the function equivalents to the $bp->current_action and $bp->action_variables[0] tests.

I also added isset checks to the $_POST variable checks in the admin section. I was getting PHP warnings that those not checked weren't set.