I was trying to generate URIs for Bookmarks based on (profile, crc32(url), created).
I failed at that. CRC32s are unsigned ints, and our schema code didn't like that.
On top of that, my code to encode and restore created timestamps was problematic.
So, I switched back to using a meaningless unique ID for Bookmarks.
One way to do this would be to use an auto-incrementing integer ID. However, we've been
kind of crabbed out a few times for exposing auto-incrementing integer IDs as URIs, so
I thought maybe using a random UUID would be a better way to do it.
So, this patch sets random UUIDs for URIs of bookmarks.
Had some problems with PuSH and Salmon use of Bookmarks; they were
being required to generate Atom versions of the bookmark _before_ the bookmark was saved.
So, I reversed the order of how things are saved, and associate notices and bookmarks
by URI rather than notice_id.
