Merge pull request #12 from carleton/CONTRIB-4878

CONTRIB-4878: url escape mailto links
CONTRIB-5018 Fix creation of slots when Force Overlap is selected
PostgreSQL compatibility
Only try deleting the calendar events if the id is defined
Fix some inconsistencies in SQL requests building
In scheduler_get_attendants, use user_picture::fields to make sure fullname() always works
Use user_picture::fields everywhere possible instead of hardcoding the user name fields
CONTRIB-5182 E-mail language formatting
Partial fix: Sending e-mail in recipient's preferred language