overriding message suppression, revisited

This is more robust than the previous hack.  The issue of whether to
use it in other places is still unexplored.  Ultimately it's the user's
fault if overzealous message suppression hides something important.
[For an eerie game, try 'MSGTYPE=hide .'.]

src/options.c

@@ -1500,6 +1500,8 @@ boolean norepeat; /* called from Norep(via pline) */
     struct plinemsg_type *tmp = plinemsg_types;
 
     while (tmp) {
+        /* we don't exclude entries with negative msgtype values
+           because then the msg might end up matching a later pattern */
         if (regex_match(msg, tmp->regex))
             return tmp->msgtype;
         tmp = tmp->next;
@@ -1507,6 +1509,26 @@ boolean norepeat; /* called from Norep(via pline) */
     return norepeat ? MSGTYP_NOREP : MSGTYP_NORMAL;
 }
 
+/* negate one or more types of messages so that their type handling will
+   be disabled or re-enabled; MSGTYPE_NORMAL (value 0) is not affected */
+void
+hide_unhide_msgtypes(hide, hide_mask)
+boolean hide;
+int hide_mask;
+{
+    struct plinemsg_type *tmp;
+    int mt;
+
+    /* negative msgtype value won't be recognized by pline, so does nothing */
+    for (tmp = plinemsg_types; tmp; tmp = tmp->next) {
+        mt = tmp->msgtype;
+        if (!hide)
+            mt = -mt; /* unhide: negate negative, yielding positive */
+        if (mt > 0 && ((1 << mt) & hide_mask))
+            tmp->msgtype = -tmp->msgtype;
+    }
+}
+
 int
 msgtype_count()
 {