table resolution".
Added members to Item_ident for storing original db, table and field
names since those that set later from Field have shorter life-time 
than required by prep. stmt. So we need to restore original names in 
Item_ident::cleanup(). Also now using special construnctor for creation
of Item_field from Field object that ensures that table and field name 
have big enough life-time.

"Fix" for bug #2050 "10 to 1 performance drop with server 4.1.1"
Clean ups in implementation of caching of field number in table.
Added caching of table in which field is found in find_field_in_tables(). 


sql/item.cc:
  Added members to Item_ident for storing original db, table and field
  names since those that set later from Field have shorter life-time 
  than required by prep. stmt. So we need to restore original names in 
  Item_ident::cleanup().
  Added Item_ident::cached_table for caching table there we found 
  our field.
  Added special constructor for creation of Item_field from Field object
  that ensures that table and field name have big enough life-time.
sql/item.h:
  Added members to Item_ident for storing original db, table and field
  names since those that set later from Field have shorter life-time 
  than required by prep. stmt. So we need to restore original names in 
  Item_ident::cleanup().
  Changed type of Item_ident::cached_field_index from int to uint
  (and so NO_CACHED_FIELD_INDEX is UINT_MAX now) because we want to
  save one comparison in find_field_in_table().
  Added Item_ident::cached_table for caching table there we found 
  our field.
  Added special constructor for creation of Item_field from Field object
  that ensures that table and field name have big enough life-time.
sql/mysql_priv.h:
  Changed type of cached_field_index_ptr from int* to uint*
  (and so NO_CACHED_FIELD_INDEX is UINT_MAX now) because we want to
  save one comparison in find_field_in_table().
sql/sql_acl.cc:
  Changed type of find_field_in_table() paremeter to make it 
  faster.
sql/sql_base.cc:
  find_field_in_table(): small optimization and soime clean ups in 
   caching of field index.
  find_field_in_tables(): added aggresive caching of table in which
   field is found in Item_ident::cached_table.
  insert_fields():
   using special construnctor for creation of Item_field from Field 
   object that ensures that table and field name have big enough life-time.