Geometry fields have a result type string and a 
  special subclass to cater for the differences
  between them and the base class (just like 
  DATE/TIME).
  When creating temporary tables for results of 
  functions that return results of type GEOMETRY
  we must construct fields of the derived class 
  instead of the base class.
  Fixed by creating a GEOMETRY field (Field_geom) 
  instead of a generic BLOB (Field_blob) in temp 
  tables for the results of GIS functions that 
  have GEOMETRY return type (Item_geometry_func).


mysql-test/r/gis.result:
  Bug #27300: test case
mysql-test/t/gis.test:
  Bug #27300: test case
sql/item.cc:
  Bug #27300:
    Create a GEOMETRY field (Field_geom) instead of 
    a generic BLOB (Field_blob) in temp tables for 
    the results of GIS functions (Item_geometry_func).
sql/sql_select.cc:
  Bug #27300:
    Create a GEOMETRY field (Field_geom) instead of 
    a generic BLOB (Field_blob) in temp tables for 
    the results of GIS functions (Item_geometry_func).