Extend units.lib with prefixes from Resolution 3 of the 27th meeting of CGPM.

Some more corrections/additions in units.lib:

1. cables; US cables are 720 ft, but international cables are 1/10
nautical mile and UK Admiralty cables are 1/10 of 1853.2 meters
instead of 1852 meters. Make "cable" refer to the international
definition, and add "uscable" and "admiraltycable".

2. rods and chains. US rods and chains and furlongs are defined in
terms of US survey feet, not international feet. Since the US is
apparently working on retiring survey feet, it seems like the best way
forward on this is to define two sets of these units, one prefixed
with "us". Also since this file was inconsistent about using "survey"
vs. "surveyors", fill in more duplicates.

Furthermore, Gunter's rods and chains and links are as best I can tell
the same as the international ones, so since we already have
"gunterschain" add "guntersrod" and "gunterslink".

3. If we're going to make pf a special abbreviation for picofarad,
it's reasonable to make uf a special abbreviation for microfarad, and
if we're going to define "meg" for "megabyte" we should also have
"gig".

4. A "franklin" _is_ a statcoulomb, not an approximation of one.

5. "jewel" has two Es.

units.lib: fix "surveyfoot" and kill off "british".

The US survey foot is defined as 1200/3937 of a meter, whereas the
ordinary international foot is 0.3048 meter. These are almost, but
not quite the same.

Define the survey foot this way instead of defining an adjective unit
for the conversion, which is much less confusing even if the adjective
unit had a reasonable name. For the time being the fact that it was
called "british" remains thoroughly obscure.

Reorganize units.lib.

It's all very well to file miscellaneous old units under "trivia" but
it's more useful to sort first by type and then by creakiness.

No functional change intended.

Define becquerels in base units (like curies and rutherfords already are),
rather than in terms of curies.

Add symbol Bq for becquerel.

fix inconsistent whitespace in units.lib

If we're having Thai units, make them correct. A tarangwah is a square wah,
which is ~4m^2 but not exactly (just as a wah is not exactly 2m, but close).
(wah apparently comes from the width of a person with hands outstretched...)

Add troyounce

On second thought, don't include more than one spelling for thai units

Add more Thai length, area and weight units

Add most common thai length/area measurements of wah rai ngan

branches: 1.19.2; 1.19.4;
File watt in the right group, and accept W as well, as that's quite
standard.

Add tera- and peta-bytes.

Rename "tappit-hen" to "tappithen" because unit names cannot contain
hyphens. Also change the definition from "3 imperial" (a dimensionless
quantity) to "3 bottle" (2.25 litres). Wikipedia and several other web
sites say 3 bottles or 2.25 litres, but
<http://www.christies.com/lotfinder/wine/chateau-lafite-rothschild-vintage-1811-1-tappit-hen-per-4992576-details.aspx>
says:

There seems to be no firm definition of the bottle size referred to
as "tappit-hen". Believed to be of Scottish origin, a tappit-hen
can vary, according to which definition one follows, from 1 1/2
bottles to a tregnum or 3-bottle bottle. It is safest to say that it
approximates to a magnum.

and ends with:

1 Tappit-Hen (2.25 liters) per lot

Fix references to undefined units:
* "southamericarand" should be "southafricarand";
* "sidereal day" should be "siderealday";
* "perusol" should be "perunewsol".

branches: 1.15.4; 1.15.10;
Update radioactivity-related units from http://physics.nist.gov/cuu/Units/.
The prior definition of sievert was, as far as I can tell, entirely wrong.

Caution: while "gray" and "sievert" have the same dimensionality,
they're not interchangeable -- you need to multiply by a fudge factor
that varies depending on the type of radiation and the tissue it's
affecting. (Dimensional analysis is often not a substitute for knowing
what you're doing.)

It would be nice if units had a way to warn users when they're trying
to do something that doesn't make sense, since there are lots of ways
to do so, but it doesn't, and it wouldn't be easy to arrange in the
general case.

dipotre -> dioptre.
(nobody's noticed this typo since the file was originally added in 1993...)

A hogshead is defined in the U.S. to be 63 gallons, and otherwise refers
to a volume unit of varying capacity (betwen 63 and 140(!)) gallons.

Since the U.S. is the only place it is defined, and I can find little
evidence to support the "barrel" definition, make it 63 gallons.

Like everything, this was prompted by the Simpsons.

"The metric system is a tool of the devil! My car gets 40 rods to the
hogshead, and that's the way I likes it!"

-- Abe Simpson

Remove jeroboam, magnum, and rehoboam from the "trivia" section and
put them in another section with all the other bottles (the new aptly
named "bottles" section).

Also, add shed (1e-24 barn).

add the smoot

Add ``score'' (20) to trivia section.

While I'm here, for those currencies that have a fixed exchange rate against
the Euro (BEF, DEM, ESP, FRF, IEP, ITL, LUF, NLG, ATS, PTE, FIM, GRD), use
that exchange rate.

Add "rackunit" (alias "RU" or "U").

Add 's' to netherlandguilder. Fixes bin/12082 by Benjamin Wong.

Tyop: millennium, not millenium (FreeBSD PR/24369)

Add euro, per PR 6898 by Anders Magnusson <ragge@ludd.luth.se>
Value taken from www.deutsche-bank.de.

RCS ID police

RCS Id police.

fix bugs (missing spaces) in definitions of nmile an Xunit, as pointed
out by John F. Woods <jfw@jfwhome.funhouse.com>.

add units command, written by Adrian Mariano (adrian@cam.cornell.edu or
mariano@geom.umn.edu), cleaned up, KNF'd, etc., by cgd