Safety fix to not allow one to specify too big max_alloc_packet to mysqld

Safety fix to not cause conflicts with extended packages in 4.0.


sql/mysqld.cc:
  Safety fix to not allow one to specify too big max_alloc_packet
sql/net_serv.cc:
  Safety fix to not cause conflicts with extended packages in 4.0.
  (Should not cause any notable changes for 3.23 servers)

sql/mysqld.cc

@@ -2984,7 +2984,7 @@ CHANGEABLE_VAR changeable_vars[] = {
 #endif
     ,0, 1, 0, 1 },
   { "max_allowed_packet",      (long*) &max_allowed_packet,
-      1024*1024L, 80, 64*1024*1024L, MALLOC_OVERHEAD, 1024 },
+      1024*1024L, 80, 16*1024*1024L, MALLOC_OVERHEAD, 1024 },
   { "max_binlog_cache_size",   (long*) &max_binlog_cache_size,
       ~0L, IO_SIZE, ~0L, 0, IO_SIZE },
   { "max_binlog_size",         (long*) &max_binlog_size,

sql/net_serv.cc

@@ -40,7 +40,7 @@ ulong max_allowed_packet=65536;
 extern ulong net_read_timeout,net_write_timeout;
 extern uint test_flags;
 #else
-ulong max_allowed_packet=16*1024*1024L;
+ulong max_allowed_packet=16*1024*1024L-1;
 ulong net_read_timeout=  NET_READ_TIMEOUT;
 ulong net_write_timeout= NET_WRITE_TIMEOUT;
 #endif