Distinguish hyphen from minus from dashes.

Most of this patch is to commentary, to distinguish better among
the similar characters hyphen '-', minus sign '−', en dash '–' (used
for ranges), and em dash '—'.  Render ordinary dashes in text as
spaced en dashes, as this gives better-looking results in monospaced
fonts.
* yearistype.sh, zic.c: Reword diagnostics so that they do not use
hyphens as if they were dashes.  Since we are sticking to ASCII in
programs, we can't use proper dashes in diagnostics.

tz-art.htm

@@ -317,7 +317,7 @@ O'Clock, Eastern Wartime</a></td></tr>
 Mystery, history, daylight saving time, and old-time radio.
 </td></tr>
 <tr><td>&nbsp;</td></tr>
-<tr><td>Film</td><td>Bell Science - About Time</td></tr>
+<tr><td>Film</td><td>Bell Science – About Time</td></tr>
 <tr><td>Notes</td><td>The Frank Baxter/Richard Deacon extravaganza.
 Information is available at
 <a href="http://www.videoflicks.com/titles/1035/1035893.htm">http://www.videoflicks.com/titles/1035/1035893.htm</a></td></tr>
@@ -438,7 +438,7 @@ as noted by Will Fitzgerald)
 </li>
 <li>
 Brady: "...[Bishop Usher] determined that the Lord began the Creation
-on the 23rd of October in the Year 4004 B.C. at -- uh, at 9 A.M.!"
+on the 23rd of October in the Year 4004 B.C. at – uh, at 9 A.M.!"
 <br>
 Drummond: "That Eastern Standard Time? (Laughter)  Or Rocky Mountain
 Time? (More laughter)  It wasn't daylight-saving time, was it?  Because