Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Convert block comments into C-style that is understood by cpp(1).
Keep line comments in assembler style. A few lines that match
the '^[[:space:]]+#' regexp still need to be fixed, somehow.

OK'ed by: bde, jhb

- Properly merge boot0sio.s and boot0.s into boot0.S.
boot0sio.s was repo-copied to boot0.S.

- Rename boot0ext.s to boot0ext.S, to stay consistent
with other preprocessed asm files around here, and
for better portability.

Repocopied by: joe

Fix a last second typo in 'vi' that caused a problem.

White space style cleanup.

Rev 1.2 changes include:
- Merge support for numeric keys 1-5 from boot0.s
- Fix _PRTEND for the case of more than 2 sectors.
- Move the code to set the drive number up before we try to load in the rest
of boot0 off of the disk.
- Expand the OS name table to recognize more windows partitions and rename
the NT entry to 'Windows NT/XP'.

MFp4: merge version #5 of the 2-sector boot0 from the "jhb boot" branch.

Bring back jhb's two sector (1024 bytes) 'boot0' [rev 1.22] as 'boot0ext'.