Tweaked alert dialogs. Clicking 'x' issues a response. Either 'close', 'cancel', 'ok' or a dummy 'close' which will result in LLNotification::getSelectedOption returning -1 in callback. Listed in order of preference.
Disable AA when drawing ui.
Fix some subtle bugs in llrender.
Avoid using invalid iterator in LLNotifications::getChannel if channel is not found.
Renamed SHAlphaMaskMaxRMSE to SHAutoMaskMaxRMSE. Disabled alpha masking on attachments.