* src/video_output/video_output.c: moved some stuff to vout_IntfInit().
* include/video_output.h: vout_vaControl()/vout_Control() prototypes.
* modules/video_output/x11/xcommon.c: implemented a vout_Control() (only VOUT_SET_ZOOM for now).
* modules/gui/wxwindows/menus.cpp: handle float object vars, added "zoom" to the menus.