* conf/i386-pc.rmk (pxeboot_img_LDFLAGS): The text address should
be 0x7C00 instead of 0x8000.
* boot/i386/pc/pxeboot.S: Rewritten.
* kern/i386/pc/startup.S (gate_a20_try_bios): No need to specify
EXT_C.
(gate_a20_check_state): Read a byte from 0x108000. Invert the
result.
* conf/i386-pc.rmk (pkgdata_IMAGE): Add pxeboot.img.
(pxeboot_img_SOURCES): New variable.
(pxeboot_img_ASFLAGS): Likewise.
(pxeboot_img_LDFLAGS): Likewise.
* boot/i386/pc/pxeboot.S: New file. Based on pxeloader.S from
GRUB Legacy and boot.S. Adopted for GRUB 2 by lode leroy
<lode_leroy@hotmail.com>.