Clarify infrun variable naming.

	Clarify infrun variable naming.
	* infrun.c (trap_expected): Rename
	to stepping_over_breakpoint.  Document.
	(stepping_past_breakpoint): Remove.
	(stepping_past_breakpoint_ptdi): Renamed
	to deferred_step_ptid.
	(struct execution_control_state): Rename
	the another_trap field to stepping_over_breakpoint.
	(struct inferior_status): Rename the trap_expected
	field to stepping_over_breakpoint.
	(clear_proceed_status, proceed)
	(init_execution_control_state, context_switch)
	(handle_inferior_event, currently_stepping)
	(keep_going, save_inferior_status)
	(restore_inferior_status, prepare_to_proceed): Adjust.
	* gdbthread.h (struct thread_info): Rename the
	trap_expected field to stepping_over_breakpoint.
	* thread.c (load_infrun_state, save_infrun_state):
	Adjust.