Switch cache creation APIs to the two-pool paradigm if they use temporaries.
Update callers, FSFS cache init code in particular.

* subversion/include/private/svn_cache.h
  (svn_cache__make_memcache_from_config,
   svn_cache__create_membuffer_cache): Add a scratch pool parameter.

* subversion/libsvn_subr/cache-memcache.c
  (svn_cache__make_memcache_from_config): Replace the temporary sub-pool
                                          with the new scratch pool.

* subversion/libsvn_subr/cache-membuffer.c
  (svn_cache__create_membuffer_cache): Allocate temporaries in the scratch
                                       pool.

* subversion/libsvn_fs_fs/caching.c
  (create_cache): Switch to two-pool paradigm and pass them along
                  to the modified APIs.
  (svn_fs_fs__initialize_caches): Provide the scratch pool.
  (svn_fs_fs__initialize_txn_caches): Trivially adapt to API change.

* subversion/libsvn_fs_fs/fs_fs.c
  (read_config): Provide a scratch pool.

* subversion/libsvn_fs_x/caching.c
  (read_config): Same.
  (create_cache): Trivially adapt to API change.

* subversion/tests/libsvn_subr/cache-test.c
  (test_memcache_basic,
   test_membuffer_cache_basic,
   test_memcache_long_key): Same.

* tools/server-side/fsfs-stats.c
  (read_revisions): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1590482 13f79535-47bb-0310-9956-ffa450edef68