mod_dav_fs: add DAVLockDBType directive.

mod_dav_fs: add DAVLockDBType directive.

* modules/dav/fs/dbm.c (dav_dbm_open_direct): Take a dbmtype argument
  and use it to select the apr_dbm driver type.
  (dav_dbm_open): Continue to use the "default" propdb type to open
  the property databases.

* modules/dav/fs/lock.c: Store and pass through the lockdb_type
  through.

* modules/dav/fs/mod_dav_fs.c (dav_get_lockdb_path): Return the dbm
  type via an output argument.
  (dav_fs_cmd_davlockdbtype): New config directive.
  (dav_fs_merge_server_config): Merge the dbm type.
  (dav_fs_post_config): Set the default lockdb type.

* modules/dav/fs/repos.h: Update prototypes as above; internal API
  only so no compat concerns.

Github: closes #386

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1912718 13f79535-47bb-0310-9956-ffa450edef68