- avoid notice spew when checking sreg items that weren't provided
- fix keys spec for user_openid, clears up problems with removing openid associations
- fix keys spec for user_openid_trustroot
- avoid notice on insert (missing sequenceKeys())
- avoid cache corruption on delete (user_id was missing from keys list, cache not cleared for user_id lookups)
As a first step to pluginizing our OpenID support, I've moved the
important OpenID-related files to a dedicated plugin directory. Many
of these classes are still referred to by libraries that are still in
core.
