Changed the parser test for wildcards in hostname to checking for empty
strings instead (analogous with the test in default_view_definer()),
since wildcards do appear in the definer's host-part sometimes.
Item_type_holder doesn't store information about length and exact type of
original item which results in redefining length to max_length and geometry
type to longtext.
Changed the way derived tables except unions are built. Now they are created
from original field list instead of list of Item_type_holder.
