Factor out a bit of FSFS code.
Factor out a bit of FSFS code.

* subversion/libsvn_fs_fs/fs_fs.c
  (write_revnum_file): New function.
  (pack_shard, pack_revprop_shard): Use it instead of inline code.

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