osdb: Expand to cover the entire interface.
guru: Hack up a guru for OSDB.
namer: Add the original extension into the formatting data.
Fixups to make OSDB guru work.
namer: Adjust extension slightly.
guru: Actually use IGuru, and test to verify.
Move FileNotFound down to the backends.

Removes a couple stringly-typed cases.
guru: Hack for OSDB file sizes.