xC: regard more characters as highlight delimiters

Almost 10 years of a poor decision.

xC.c

@@ -7034,9 +7034,7 @@ irc_is_highlight (struct server *s, const char *message)
 	cstr_transform (nick, s->irc_tolower);
 
 	// Special characters allowed in nicknames by RFC 2812: []\`_^{|} and -
-	// Also excluded from the ASCII: common user channel prefixes: +%@&~
-	// XXX: why did I exclude those?  It won't match when IRC newbies use them.
-	const char *delimiters = ",.;:!?()<>/=#$* \t\r\n\v\f\"'";
+	const char *delimiters = "\t\n\v\f\r !\"#$%&'()*+,./:;<=>?@~";
 
 	bool result = false;
 	char *save = NULL;