add comment about an ugly hack

ps/parser.c

@@ -226,6 +226,11 @@ static const char *parse_sysv_option(void){
     // This list of options is ONLY for those defined by the
     // "IEEE Std 1003.1, 2004 Edition", "ISO/IEC 9945:2003",
     // or "Version 2 of the Single Unix Specification".
+    //
+    // It may be time to re-think the existance of this list.
+    // In the meantime, please do not add to it. The list is
+    // intended to ONLY contain flags defined by the POSIX and UNIX
+    // standards published by The Open Group, IEEE, and ISO.
     if(!strchr("aAdefgGlnoptuU", *flagptr)) not_pure_unix = 1;
 
     switch(*flagptr){