Revision to this change--use ->next != NULL, not just ->next, when

Revision to this change--use ->next != NULL, not just ->next, when
passing an integer argument to find_pc_line.

	* frame.h, blockframe.c, stack.c, a29k-tdep.c,
	config/gould/tmp-{pn,np1}.h,
	config/{sparc/tm-sparc.h,pyr/tm-pyr.h,vax/tm-vax.h}: Remove field
	next_frame from struct frame_info.  It has no purpose beyond
	->next->frame and is an artifact from GDB 2.8.