Add unicode_*_linestyle to \? variables

In a2dabf0e we added the ability to have single or double unicode
linestyle for the border, column, or header.  Unfortunately, the
\? variables output was not updated for these new psql variables.

This corrects that oversight.

Patch by Pavel Stehule.

src/bin/psql/help.c

@@ -305,7 +305,7 @@ helpVariables(unsigned short int pager)
 {
 	FILE	   *output;
 
-	output = PageOutput(81, pager);
+	output = PageOutput(85, pager);
 
 	fprintf(output, _("List of specially treated variables.\n"));
 
@@ -364,6 +364,10 @@ helpVariables(unsigned short int pager)
 					 "                     column width of left aligned data type in latex format\n"));
 	fprintf(output, _("  title              set the table title for any subsequently printed tables\n"));
 	fprintf(output, _("  tuples_only        if set, only actual table data is shown\n"));
+	fprintf(output, _("  unicode_border_linestyle\n"));
+	fprintf(output, _("  unicode_column_linestyle\n"));
+	fprintf(output, _("  unicode_header_linestyle\n"
+					 "                     set the style of unicode line drawing [single, double]\n"));
 
 	fprintf(output, _("\nEnvironment variables:\n"));
 	fprintf(output, _("Usage:\n"));