When man pages are formatted in UTF-8, .Fl is encoded as U+2212 "MINUS

SIGN" instead of U+002D "HYPHEN-MINUS".  This is unfortunate for two
reasons: 1) this is not the character which is actually used on the
command line, and 2) it makes it impossible to search a man page for a
specific command-line option.

This patch fixes this, but there are other unresolved issues, such as
confusion between -, \- and hy: while the latter is always (and only)
used for hyphenation, both - and \- are used for negation and
subtraction, and \- is used for command-line options and sometimes
also for parenthesis.  IMHO, the correct Unicode characters are:

 - hyphenation: either U+2010 or U+00AD, most likely the former (the
   latter is the so-called soft hyphen, used to indicate a point at
   which a text processor is allowed to hyphenate a word)

 - negation and subtraction: U+2212

 - parenthesis: in English, U+2214, with spaces suppressed before and
   after; in some others (such as Norwegian), U+2213 with spaces
   retained.

 - command-line options: U+002D, because that is what is actually used
   on the command line.

However, fixing this would require extensive modifications to (at least)
the doc and man macro sets...

MFC after:	1 week

contrib/groff/font/devutf8/R.proto

@@ -726,7 +726,7 @@ st	24	0	0x220B
 product	24	0	0x220F
 coproduct	24	0	0x2210
 sum	24	0	0x2211
-\-	24	0	0x2212
+\-	24	0	0x002D
 mi	"
 -+	24	0	0x2213
 **	24	0	0x2217