On the fsfs-format7 branch:  Define a policy on what priorities should
be assigned to our caches and ajust priorities accordingly 

* subversion/libsvn_fs_fs/caching.c
  (svn_fs_fs__initialize_caches): document policy and adjust priorities

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1477176 13f79535-47bb-0310-9956-ffa450edef68