Fixed compiler warnings from gcc 4.0.2:

- Added empty constructors and virtual destructors to many classes and structs
- Removed some usage of the offsetof() macro to instead use C++ class pointers


configure.in:
  Added comment
ndb/include/ndbapi/NdbDictionary.hpp:
  Fixed compiler warnings from gcc 4.0.2
sql/field.cc:
  Fixed compiler warnings from gcc 4.0.2
sql/handler.h:
  Fixed compiler warnings from gcc 4.0.2
sql/item.h:
  Fixed compiler warnings from gcc 4.0.2
sql/item_cmpfunc.h:
  Fixed compiler warnings from gcc 4.0.2
sql/log_event.h:
  Fixed compiler warnings from gcc 4.0.2
sql/mysql_priv.h:
  Fixed compiler warnings from gcc 4.0.2
  For find_table_in_list I fixed it to use proper C++ class pointers instead of C style pointers
sql/opt_range.cc:
  Fixed compiler warnings from gcc 4.0.2
sql/parse_file.h:
  Fixed compiler warnings from gcc 4.0.2
sql/sp_rcontext.h:
  Fixed compiler warnings from gcc 4.0.2
sql/spatial.h:
  Fixed compiler warnings from gcc 4.0.2
sql/sql_base.cc:
  Fixed compiler warnings from gcc 4.0.2
sql/sql_cache.h:
  Fixed compiler warnings from gcc 4.0.2
sql/sql_class.h:
  Fixed compiler warnings from gcc 4.0.2
sql/sql_parse.cc:
  Fixed compiler warnings from gcc 4.0.2
  (Not pretty, but seams to work...)
sql/sql_select.h:
  Fixed compiler warnings from gcc 4.0.2
sql/sql_update.cc:
  Fixed compiler warnings from gcc 4.0.2
sql/table.h:
  Fixed compiler warnings from gcc 4.0.2
sql/tztime.cc:
  Fixed compiler warnings from gcc 4.0.2
sql/tztime.h:
  Fixed compiler warnings from gcc 4.0.2

sql/item.h

@@ -164,7 +164,8 @@ struct Hybrid_type_traits
   virtual my_decimal *val_decimal(Hybrid_type *val, my_decimal *buf) const;
   virtual String *val_str(Hybrid_type *val, String *buf, uint8 decimals) const;
   static const Hybrid_type_traits *instance();
-  Hybrid_type_traits() {};
+  Hybrid_type_traits() {}
+  virtual ~Hybrid_type_traits() {}
 };
 
 
@@ -339,6 +340,7 @@ private:
   bool        save_resolve_in_select_list;
 
 public:
+  Name_resolution_context_state() {}          /* Remove gcc warning */
   TABLE_LIST *save_next_local;
 
 public:
@@ -1015,6 +1017,7 @@ bool agg_item_charsets(DTCollation &c, const char *name,
 class Item_num: public Item
 {
 public:
+  Item_num() {}                               /* Remove gcc warning */
   virtual Item_num *neg()= 0;
   Item *safe_charset_converter(CHARSET_INFO *tocs);
 };