Add a generic locking provider to DAV - mod_dav_lock. Other DAV providers can use the dav_hooks_locks_generic structure to implement locking in a non-optimal, but compliant fashion. (Use 'dav-lock', 'generic', '0' to ap_lookup_provider to retrieve it.) Use the DavGenericLockDB directive to configure the location of the lock database (may be server-relative or absolute). This allows all DAV providers to use a baseline locking API rather than roll their own. This code is based mainly off the mod_dav_fs locking code (which uses the on-disk storage for locking), but removing components that aren't needed in a non-file-backed repository (such as recording inodes).