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

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

Add missing static keywords to units(1)

Add limited support for units that are related by affine rather
than linear relations. We can now convert degC to degF.

586 units, 56 prefixes
You have: 24 degC
You want: degF
75.2
You have: degC
You want: K
(-> x*1 +273.15)
(<- y*1 -273.15)

Add enough consts to keep everyone happy.

Add prototypes and turn on WARNS=?2.

Give units a bit of a cleanup:

1) Fix a bug where the recursion on prefixes where if recusrion failed
then the next attempt started too far along the string.
2) Up some internal limits that we were about to hit off.
3) Change the constness and signedness of some things and complete missing
prototypes.
4) Remove the readerror function 'cos it could print out the wrong
wrong file name. Replace it with more useful error messages.
5) Use sizeof when passing buffers to fgets.
6) Warn about empty prefix definitions.

Reviewed by: iedowse

Don't segv when trying to add a 0-length unit name.
Some string-related cleanups inspired by OpenBSD.

Reviewed by: asmodai

$Id$ -> $FreeBSD$

Use err(3). Cosmetic in usage(). Rewrote man page in mdoc format.

Revert $FreeBSD$ to $Id$

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.

Fix exit code when used in non-interactive mode.
Remove ';' typo attached to if statement.

This commit was generated by cvs2svn to compensate for changes in r16186,
which included commits to RCS files with non-trunk default branches.

Units conversion utility courtesy of NetBSD.

Submitted by: Jeremy Prior
Obtained from: NetBSD