Extracted the code for setting a new original avatar to the Profile
class, and moved some of it to Avatar, too. This makes it easier to
have the same functionality whether an avatar is set using the profile
settings (for our users), or on a remote subscription. Necessitated
changing the filenaming function to just take an ID.
darcs-hash:20080605193708-84dde-a441cc0474951ce7f1a1da9310b5145c0b7c3070.gz
