parse-options: localize mark-up of placeholder text in the short help

i18n: expose substitution hint chars in functions and macros to
translators

For example (based on builtin/commit.c and shortened): the "--author"
option takes a name.  In source this can be represented as:

  OPT_STRING(0, "author", &force_author, N_("author"), N_("override author")),

When the command is run with "-h" (short help) option (git commit -h),
the above definition is displayed as:

  --[no-]author <author>    override author

Git does not use translated option names so the first part of the
above, "--[no-]author", is given as-is (it is based on the 2nd
argument of OPT_STRING).  However the string "author" in the pair of
"<>", and the explanation "override author for commit" may be
translated into user's language.

The user's language may use a convention to mark a replaceable part of
the command line (called a "placeholder string") differently from
enclosing it inside a pair of "<>", but the implementation in
parse-options.c hardcodes "<%s>".

Allow translators to specify the presentation of a placeholder string
for their languages by overriding the "<%s>".

In case the translator's writing system is sufficiently different than
Latin the "<>" characters can be substituted by an empty string thus
effectively skipping them in the output.  For example languages with
uppercase versions of characters can use that to deliniate
replaceability.

Alternatively a translator can decide to use characters that are
visually close to "<>" but are not interpreted by the shell.

Signed-off-by: Alexander Shopov <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: alshopov

parse-options.c

@@ -1076,11 +1076,23 @@ static int usage_argh(const struct option *opts, FILE *outfile)
 		!opts->argh || !!strpbrk(opts->argh, "()<>[]|");
 	if (opts->flags & PARSE_OPT_OPTARG)
 		if (opts->long_name)
-			s = literal ? "[=%s]" : "[=<%s>]";
+			s = literal ? "[=%s]" :
+			  /* TRANSLATORS: %s is a command line argument name, `<>' prompt the user to supply a value for it.
+			     Change only the `<>' characters to something else if you use another convention for this.
+			     Most translations leave this message as is. */
+			  _("[=<%s>]");
 		else
-			s = literal ? "[%s]" : "[<%s>]";
+			s = literal ? "[%s]" :
+			  /* TRANSLATORS: %s is a command line argument name, `<>' prompt the user to supply a value for it.
+			     Change only the `<>' characters to something else if you use another convention for this.
+			     Most translations leave this message as is. */
+			  _("[<%s>]");
 	else
-		s = literal ? " %s" : " <%s>";
+		s = literal ? " %s" :
+		  /* TRANSLATORS: %s is a command line argument name, `<>' prompt the user to supply a value for it.
+		     Change only the `<>' characters to something else if you use another convention for this.
+		     Most translations leave this message as is. */
+		  _(" <%s>");
 	return utf8_fprintf(outfile, s, opts->argh ? _(opts->argh) : _("..."));
 }