make default range be 1900-2100
regardless of everything else, rules that recur forever finish at world_end
caldav_db: stupid reuse bugs again
greedymatch to avoid re-expanding and failing on the recurrence rule
caldav_alarm: lock DB with a namelock, and hold open for shortest time
make world_start and world_end be in UTC explicitly

Fixes stupidity with single-ended date ranges and iOS
http_dav: abort early if no mailbox parts at all
imapparse: handle RETURN ()