* infrun.c: Remove step_resume_{duplicate,shadow}. Replace

	* infrun.c: Remove step_resume_{duplicate,shadow}.  Replace
	step_resume_break_address with step_resume_breakpoint (now local
	to wait_for_inferior).
	({insert,remove}_step_breakpoint): Remove.
	(wait_for_inferior): Set step resume break with
	set_momentary_breakpoint.  Test hitting it with bpstat_stop_status
	and bpstat_what	(stop_step_resume_break removed).
	* breakpoint.{h,c}, infrun.c: Return value from bpstat_what now struct
	which includes previous return value as main_action, and a step_resume
	bit.
	* breakpoint.c (delete_breakpoint): If breakpoint was inserted, and
	there is another breakpoint there, insert it.
	* infrun.c (wait_for_inferior): Rearrange the spaghetti a bit.  Use
	a few more gotos.
	Various: Clean up and add comments.