There's no good reason for an RA API to return a "feature not implemented" error
and then leave callers to rig up some kind of fallback mechanism. If such a
fallback mechanism can be rigged, we should put it into the RA loader module so
that API is as complete as possible.
In r27095, I did this with the svn_ra_get_locations() fallback implementation.
But we still have a fallback implementation of svn_ra_get_file_revs() that lives
in libsvn_client/blame.c.
The work here is probably a little tedious, but shouldn't be difficult.
Major