i16_raw.c:
	Provides a default implementation
	of real/pmode switching code.
	Assumes that, as far as it's concerned,
	low linear address always map to physical addresses.
	(The low linear mappings can be changed,
	but must be changed back before switching back to real mode.)

	Provides:
		i16_raw_switch_to_pmode()
		i16_raw_switch_to_real_mode()

		i16_raw_start()
			Called in real mode.
			Initializes the pmode switching system,
			switches to pmode for the first time,
			and calls the 32-bit function raw_start().

	Depends on:

		paging.h:
			raw_paging_enable()
			raw_paging_disable()
			raw_paging_init()

		a20.h:
			i16_enable_a20()
			i16_disable_a20()

		real.h:
			real_cs