Correct some UTC-vs-UT solecisms.

In several places the code and documentation incorrectly used
"UTC" to describe time stamps that might precede the introduction
of UTC and for which UTC is therefore undefined.  Change these
uses to "UT", as that's the correct term when talking about these
time stamps.  Problem reported by Steve Allen in
<http://mm.icann.org/pipermail/tz/2013-September/019907.html>.
The major compatibility issue here is with 'zdump -v'; it'll now
output "UT" instead of the possibly-incorrect "UTC".
Many files change in minor ways in the commentary.
* zdump.c (show):
* zic.c (inzsub, addtype):
In output, say "UT" rather than "UTC", since the time stamp we're
talking about might precede the introduction of UTC.

australasia

@@ -736,7 +736,7 @@ Zone Pacific/Funafuti	11:56:52 -	LMT	1901
 # 1886-1891; Baker was similar but exact dates are not known.
 # Inhabited by civilians 1935-1942; U.S. military bases 1943-1944;
 # uninhabited thereafter.
-# Howland observed Hawaii Standard Time (UTC-10:30) in 1937;
+# Howland observed Hawaii Standard Time (UT-10:30) in 1937;
 # see page 206 of Elgen M. Long and Marie K. Long,
 # Amelia Earhart: the Mystery Solved, Simon & Schuster (2000).
 # So most likely Howland and Baker observed Hawaii Time from 1935