Move grub_chainloader_real_boot out of the kernel.

	Move grub_chainloader_real_boot out of the kernel.

	* grub-core/Makefile.am: Remove machine/loader.h.
	* grub-core/kern/i386/pc/startup.S (grub_chainloader_real_boot):
	Removed.
	* grub-core/lib/i386/relocator.c (grub_relocator16_esi): New extern
	variable.
	(grub_relocator16_keep_a20_enabled): Likewise.
	(grub_relocator16_boot): Fill new variables.
	* grub-core/lib/i386/relocator16.S: Add gate a20 handling.
	* grub-core/loader/i386/pc/chainloader.c (grub_chainloader_boot): Use
	relocator.
	(grub_chainloader_unload): Likewise.
	(grub_chainloader_cmd): Likewise.
	* include/grub/i386/pc/loader.h: Removed.
	* include/grub/i386/relocator.h (grub_relocator16_state): Add a20
	and esi. All initialisers updated.