Backport of JimW's localhost patch to 4.1 tree.

Handle systems like default FC4 where 127.0.0.1 doesn't always map to 'localhost' first. 
(Bug #11822)


sql/hostname.cc:
  Short-circuit ip_to_hostname() lookup for INADDR_LOOPBACK to allways return 'localhost'.
sql/sql_parse.cc:
  Push special handling of 127.0.0.1 into ip_to_hostname().

sql/hostname.cc

@@ -130,15 +130,23 @@ void reset_host_errors(struct in_addr *in)
   VOID(pthread_mutex_unlock(&hostname_cache->lock));
 }
 
+/* Deal with systems that don't defined INADDR_LOOPBACK */
+#ifndef INADDR_LOOPBACK
+#define INADDR_LOOPBACK 0x7f000001UL
+#endif
 
 my_string ip_to_hostname(struct in_addr *in, uint *errors)
 {
   uint i;
   host_entry *entry;
   DBUG_ENTER("ip_to_hostname");
+  *errors= 0;
+
+  /* We always treat the loopback address as "localhost". */
+  if (in->s_addr == htonl(INADDR_LOOPBACK))
+    DBUG_RETURN((char *)my_localhost);
 
   /* Check first if we have name in cache */
-  *errors=0;
   if (!(specialflag & SPECIAL_NO_HOST_CACHE))
   {
     VOID(pthread_mutex_lock(&hostname_cache->lock));

sql/sql_parse.cc

@@ -696,16 +696,6 @@ static int check_connection(THD *thd)
       return (ER_OUT_OF_RESOURCES);
     thd->host_or_ip= thd->ip;
     vio_in_addr(net->vio,&thd->remote.sin_addr);
-#if !defined(HAVE_SYS_UN_H) || defined(HAVE_mit_thread)
-    /* Fast local hostname resolve for Win32 */
-    if (!strcmp(thd->ip,"127.0.0.1"))
-    {
-      thd->host= (char*) my_localhost;
-      thd->host_or_ip= my_localhost;
-    }
-    else
-#endif
-    {
     if (!(specialflag & SPECIAL_NO_RESOLVE))
     {
       vio_in_addr(net->vio,&thd->remote.sin_addr);
@@ -713,13 +703,13 @@ static int check_connection(THD *thd)
       /* Cut very long hostnames to avoid possible overflows */
       if (thd->host)
       {
+        if (thd->host != my_localhost)
           thd->host[min(strlen(thd->host), HOSTNAME_LENGTH)]= 0;
         thd->host_or_ip= thd->host;
       }
       if (connect_errors > max_connect_errors)
         return(ER_HOST_IS_BLOCKED);
     }
-    }
     DBUG_PRINT("info",("Host: %s  ip: %s",
 		       thd->host ? thd->host : "unknown host",
 		       thd->ip ? thd->ip : "unknown ip"));