Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Fix some style(9), although there's a lot more issues here.
Fix some casting errors.

PR: 142384
Submitted by: giffunip at tutopia dot com
Obtained from: NetBSD
MFC after: 3 weeks

Rename fields to match better the msdosfs headers. This work is still
incomplete as some info doesn't really belong to the structs where it is
defined.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
Reviewed by: bde
MFC after: 2 weeks

Bug fixes from NetBSD
- fix sign-compare issues.
- ANSIfy a couple of functions.
- Remove more duplicate #includes.
- Memory leak found by Coverity on NetBSD.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
Reviewed by: bde
MFC after: 2 weeks

License changes from NetBSD.
Move to 2 clause license, approved by Wolfgang Solfrank.

Submitted by: Pedro F. Giffuni <giffunip tutopia com>
MFC after: 2 weeks

Use consistent style in user prompts: the question is in a new line
and begins with a capital letter. The rest of pwarn/ask pairs here
follows this style.

Requested by: bde

Prevent the `fix?' question from running together
with the problem description on the terminal: use
conventional punctuation.

Only compare the interesting part of the bootblock with its backup.
Allow check to proceed with bad backup boot block if we're doing a
readonly check. Various typos in comments.

Obtained from: NetBSD

Forced commit to note that my previous commit was a Darwin merge.

s/filesystem/file system/g as discussed on -developers

Add fsck_msdosfs.

Obtained from: NetBSD