Fix U.S. system timezone reverting to Atlantic when the DAYLIGHT flag was set

... integer sign extension at fault here.

Also, add examples to Numeric vs. Verbal short date selection dialog.
Update some related help text.

src/sbbs3/scfg/scfgsys.c

@@ -214,7 +214,7 @@ int edit_sys_timezone(int page, int total)
 		strcpy(opt[i++],"Hawaii/Alaska");
 		strcpy(opt[i++],"Bering");
 		opt[i][0]=0;
-		switch(cfg.sys_timezone) {
+		switch(((uint16_t)cfg.sys_timezone) & ~DAYLIGHT) {
 			default:
 			case AST: i = 0; break;
 			case EST: i = 1; break;
@@ -1331,8 +1331,8 @@ int edit_sys_datefmt(int page, int total)
 	uifc.helpbuf=
 		"`Numeric Date Format:`\n"
 		"\n"
-		"If you would like abbreviated dates to be displayed in the traditional\n"
-		"U.S. date format of month first, choose `MM/DD/YY`.  If you prefer the\n"
+		"If you would like short dates to be displayed in the traditional U.S.\n"
+		"date format of month first, choose `MM/DD/YY`.  If you prefer the\n"
 		"European traditional date format of day first, choose `DD/MM/YY`.\n"
 		"If you and your users would prefer year first, choose `YY/MM/DD`.\n"
 		"\n"
@@ -1363,13 +1363,14 @@ int edit_sys_date_verbal(int page, int total)
 {
 	int mode = WIN_SAV | WIN_MID;
 	int i = cfg.sys_date_verbal;
-	char* opts[] = {
-		"Numeric", "Verbal",
-		NULL };
+	time_t t = time(NULL);
+	snprintf(opt[0],MAX_OPLN,"Numeric (e.g. %s)", unixtodstr(&cfg, (time32_t)t, tmp));
+	snprintf(opt[1],MAX_OPLN,"Verbal  (e.g. %s)", verbal_datestr(&cfg, (time32_t)t, tmp));
+	opt[2][0] = '\0';
 	uifc.helpbuf=
 		"`Short Date Display Format:`\n"
 		"\n"
-		"If you would like abbreviated dates to be displayed using verbal\n"
+		"If you would like short (8 character) dates to be displayed using verbal\n"
 		"(non-numeric, less ambiguous) month name abbreviations, choose `Verbal`.";
 	;
 	if(page) {
@@ -1378,7 +1379,7 @@ int edit_sys_date_verbal(int page, int total)
 		uifc.list_height = 2;
 	}
 	i=uifc.list(mode, 0, 11, 0,&i,0
-		,"Short Date Display Format", opts);
+		,"Short Date Display Format", opt);
 	if (i < 0)
 		return i;
 	cfg.sys_date_verbal = i;