* ./src/misc/modules.c: restored plugins hiding as the problem is fixed.
* ./plugins/directx/directx.c: UnregisterClass() in MODULE_DEACTIVATE. If
   we don't do this, trying to use the class when the plugin is reloaded will
   cause a segfault.

PS: on Win32 the sdl plugin is still affected by this. It looks like SDL keeps
    an internal state which isn't updated when we reload the plugin.