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.

europe

@@ -1863,7 +1863,7 @@ Zone	Europe/Oslo	0:43:00 -	LMT	1895 Jan  1
 # before 1895, and therefore probably changed the local time somewhere
 # between 1895 and 1925 (inclusive).
 
-# From Paul Eggert (2013-09-02):
+# From Paul Eggert (2013-09-04):
 #
 # Actually, Jan Mayen was never occupied by Germany during World War II,
 # so it must have diverged from Oslo time during the war, as Oslo was
@@ -1874,7 +1874,7 @@ Zone	Europe/Oslo	0:43:00 -	LMT	1895 Jan  1
 # 1941 with a small Norwegian garrison and continued operations despite
 # frequent air ttacks from Germans.  In 1943 the Americans established a
 # radiolocating station on the island, called "Atlantic City".  Possibly
-# the UTC offset changed during the war, but I think it unlikely that
+# the UT offset changed during the war, but I think it unlikely that
 # Jan Mayen used German daylight-saving rules.
 #
 # Svalbard is more complicated, as it was raided in August 1941 by an