* rcparse.y (control): ICON controls take an id as the first

* rcparse.y (control): ICON controls take an id as the first
parameter, not an optional string.  Also, call new convenience
function that takes res_id's.
* resrc.c (define_control): missing text means zero-length string,
not zero ID.
(define_icon_control): New.
* windres.h: declare define_icon_control.