Minor improvement.
add/addx is faster and the size remains the same.

typo in comment.

Overhaul xxboot. And merge floppy boot, taken from boot_ustar.
- Rewrite boot.S completely.
boot.S now supports boot from SCSI HD/CD and floppy.
- Use IOCS call to identify the floppy format, instead of chkfmt.s which
accesses hardware directly.
- Import print_hex() debug function from boot_ufs.
- Import a feature that displays initial registers (for debug) from boot_ufs,
and restore it (this in boot_ufs has been broken).
- Add size optimized alternatives for some libkern routines.
- Stop linking libsa to prevent to link unexpected objects.
- Bump version to 2.0.

Overhaul xxboot. And merge floppy boot, taken from boot_ustar.
- Rewrite boot.S completely.
boot.S now supports boot from SCSI HD/CD and floppy.
- Use IOCS call to identify the floppy format, instead of chkfmt.s which
accesses hardware directly.
- Import print_hex() debug function from boot_ufs.
- Import a feature that displays initial registers (for debug) from boot_ufs,
and restore it (this in boot_ufs has been broken).
- Add size optimized alternatives for some libkern routines.
- Stop linking libsa to prevent to link unexpected objects.
- Bump version to 2.0.