This makes websocket_common unload last (and near-last: rpc & websocket)
and makes us call Mod_Init for these three modules first.
This way, the period where the websocket handler is unavailable is kept
to a minimum.
This also renames the ModuleSetOptions option MOD_OPT_UNLOAD_PRIORITY
to MOD_OPT_PRIORITY since it dynamically changes the module priority
in the list. For 6.x compatibility, MOD_OPT_UNLOAD_PRIORITY can still
be used.
Bram Matthys
c3824ad47d