fsfs: make rev files (and pack files + pack manifest files) read-only.
fsfs: make rev files (and pack files + pack manifest files) read-only.

* subversion/libsvn_fs_fs/fs_fs.c
  (write_revision_zero):  Make r0 read-only.
  (commit_body):  Needs no change.
  (pack_shard):  Make the pack+manifest files read-only.

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