Refactor infrun a bit.

	Refactor infrun a bit.

	* infrun.c (currently_stepping): Take a struct
	thread_stepping_state instead of an execution_control_state.
	(struct thread_stepping_state): New, split from
	execution_control_state.
	(gtss, tss): New globals.
	(proceed): Clear the stepping state, set previous_inferior_ptid
	and clear infwait state.
	(init_wait_for_inferior): Clear the stepping state,
	previous_inferior_ptid and infwait state.
	(waiton_ptid, infwait_state): New, split from
	execution_control_state.
	(struct execution_control_state): Members that persist through
	events moved out to either struct thred_stepping_state or made
	global.  Deleted unneeded wp, saved_inferior_ptid, tmpstatus.
	(wait_for_inferior, fetch_inferior_event): Use local
	execution_control_state.  Update to execution_control_state split.
	(init_execution_control_state): Adjust.
	(init_thread_stepping_state): New, extracted from
	init_execution_control_state.
	(context_switch): Take a ptid instead of an
	execution_control_state.
	(context_switch_to): Adjust.
	(adjust_pc_after_break): Adjust.
	(init_infwait_state): New.
	(handle_inferior_event): Adjust.