Revision 1462054

On the verify-at-commit branch, add a backend-independent implementation:
a db/fs.conf file.

* subversion/include/svn_fs.h
  (SVN_FS_CONFIG_SECTION_MISC, (SVN_FS_CONFIG_OPTION_VERIFY_AT_COMMIT):
    New macros.

* subversion/libsvn_fs/fs-loader.h
  (svn_fs_t.verify_at_commit): New struct member.

* subversion/libsvn_fs/fs-loader.c
  (svn_config.h): Include.
  (CONFIG_FILENAME): New macro.
  (write_config): New helper, based on the eponymous helper in FSFS (rather
    than on write_fs_type()).
  (svn_fs_create): Call write_config().
  (fs_new): Initialise new struct member.
  (svn_fs_open): Read config.
  (svn_fs_commit_txn): Use the config.