Don't abuse "`" to mean open quote.

This was appropriate before Unicode, where "`" and "'" often balanced
in visual output, but that's been obsolete for a while.
Overall, single-quote 'like this' instead of `like this', and
double-quote "like this" or (in typeset output) “like this”
instead of ``like this''.  While we're at it, fix some glitches
with hyphens versus minus versus en dash versus em dash.
* Makefile ($(MANTXTS)): Use UTF-8 locale to produce *.txt output.
* checktab.awk, tzselect.ksh:
Quote 'like this' in diagnostics, instead of `like this'.
* date.1, newctime.3, newtzset.3, time2posix.3, zic.8 (q, lq, rq):
New macros.  Use them for better double-quoting in output.
* workman.sh: Tell Perl that its stdin and stdout are UTF-8.
* NEWS: Document this.