Slightly improve a probably rarely seen error message in FSFS.
Slightly improve a probably rarely seen error message in FSFS.

* subversion/libsvn_fs_fs/fs_fs.c
  (check_format_file_buffer_numeric): Make this function receive the entire
   buffer being parsed so it can produce a more helpful error message.
   A new OFFSET argument tells the function where to start looking for digits.
  (read_format): Update caller.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion