Make svn_fs_verify accept a FS_CONFIG parameter similar to svn_fs_open()
and svn_fs_create().  Use that in svn_repos_verify_fs2 to check FS with
the same configuration parameters that were used open opening FS.

Besides the mere symmetry aspect, this is essential use consistent cache
settings during FS verification, particularly using the same, separate
cache namespace.

* subversion/include/svn_fs.h
  (svn_fs_config): declare new API
  (svn_fs_verify): add FS_CONFIG parameter

* subversion/libsvn_fs/fs-loader.c
  (svn_fs_verify): pass the FS_CONFIG through to the FS constructor
  (svn_fs_config): implement

* subversion/libsvn_repos/dump.c
  (svn_repos_verify_fs2): use the same configuration during verification
                          as was used to open FS

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1470738 13f79535-47bb-0310-9956-ffa450edef68