Adjust item priorities such that enabling the txdelta cache by default
(as we do in 1.9) no longer impacts hot cache performance.

* subversion/libsvn_fs_fs/caching.c
  (svn_fs_fs__initialize_caches): Make the delta caches low prio as only
                                  very few operations would benefit and
                                  those would get them from L1, usually.
                                  Make all data we need for a checkout
                                  (directories, fulltext, props, revprops)
                                  standard prio items.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1580391 13f79535-47bb-0310-9956-ffa450edef68