Add support for rfc3454 casemapping

Obviously this has less than ideal performance but it should at least be correct

src/common/modes.c

@@ -840,7 +840,9 @@ inbound_005 (server * serv, char *word[], const message_tags_data *tags_data)
 		} else if (strncmp (word[w], "CASEMAPPING=", 12) == 0)
 		{
 			if (strcmp (word[w] + 12, "ascii") == 0)	/* bahamut */
-				serv->p_cmp = (void *)g_ascii_strcasecmp;
+				serv->p_cmp = g_ascii_strcasecmp;
+			else if (strcmp (word[w] + 12, "rfc3454") == 0)
+				serv->p_cmp = rfc3454_casecmp;
 		} else if (strncmp (word[w], "CHARSET=", 8) == 0)
 		{
 			if (g_ascii_strncasecmp (word[w] + 8, "UTF-8", 5) == 0)

src/common/util.c

@@ -1018,6 +1018,33 @@ make_ping_time (void)
 	return (timev.tv_sec - 50000) * 1000 + timev.tv_usec/1000;
 }
 
+/*
+ * https://tools.ietf.org/html/rfc3454
+ */
+int
+rfc3454_casecmp (const char *s1, const char *s2)
+{
+	char *s1_lower, *s2_lower, *s1_normal, *s2_normal;
+	int ret;
+
+	if (strcmp (s1, s2) == 0)
+		return 0; /* Exact same already */
+
+	s1_lower = g_utf8_casefold(s1, -1);
+	s2_lower = g_utf8_casefold(s2, -1);
+	s1_normal = g_utf8_normalize(s1_lower, -1, G_NORMALIZE_NFKC);
+	s2_normal = g_utf8_normalize(s2_lower, -1, G_NORMALIZE_NFKC);
+
+	ret = strcmp (s1_normal, s2_normal);
+
+	g_free (s1_normal);
+	g_free (s2_normal);
+	g_free (s1_lower);
+	g_free (s2_lower);
+
+	return ret;
+}
+
 
 /************************************************************************
  *    This technique was borrowed in part from the source code to 

src/common/util.h

@@ -44,6 +44,7 @@ char *file_part (char *file);
 void for_files (char *dirname, char *mask, void callback (char *file));
 int rfc_casecmp (const char *, const char *);
 int rfc_ncasecmp (char *, char *, int);
+int rfc3454_casecmp (const char *s1, const char *s2) G_GNUC_PURE;
 int buf_get_line (char *, char **, int *, int len);
 char *nocasestrstr (const char *text, const char *tofind);
 char *country (char *);