Maintenance commands to report time and space usage.

	Maintenance commands to report time and space usage.
	* main.c (display_time, display_space): New globals.
	(main): Add argument --statistics to enable reporting, display
	time and space after startup is done.
	* maint.c (maintenance_time_display, maintenance_space_display):
	New commands.
	* top.c (command_loop): Display time and space after command
	execution.

	* top.c (pre_init_ui_hook): New global.
	(gdb_init): If pre_init_ui_hook set, call before all other init.