Revision 1780939

Let the 'fsfsfixer' script accept FSFS format 6 (svn 1.8) repositories.

Since format 5 was never released (it existed in 1.7-dev builds only) and the
only change between f4 and f6 was packed revprops, and since since this script
doesn't deal with revprops, I am confident that it should work with f6 just as
well as it did with f5 or f4 -- which is to say, not perfectly but well enough
to get us out of a hole occasionally.

* contrib/server-side/fsfsfixer/fixer/fix-rev.py
  (MAX_FSFS_FORMAT): Bump from 5 to 6.