- When returning metadata for scalar subqueries the actual type of the
   column was calculated based on the value type, which limits the actual
   type of a scalar subselect to the set of (currently) 3 basic types : 
   integer, double precision or string. This is the reason that columns
   of types other then the basic ones (e.g. date/time) are reported as
   being of the corresponding basic type.
   Fixed by storing/returning information for the column type in addition
   to the result type.


mysql-test/r/subselect.result:
  Bug #11032: getObject() returns a String for a sub-query of type datetime
   - test case
mysql-test/t/subselect.test:
  Bug #11032: getObject() returns a String for a sub-query of type datetime
   - test case
sql/item_subselect.cc:
  Bug #11032: getObject() returns a String for a sub-query of type datetime
   - store and return the field type as well in addition to result type for 
     single row subqueries
sql/item_subselect.h:
  Bug #11032: getObject() returns a String for a sub-query of type datetime
   - store and return the field type as well in addition to result type for 
     single row subqueries