Now we use virtual calls instead and redirect VMT pointer of the
geometry object with 'new' operation


sql/field.cc:
  Usage of the Geometry class changed
sql/item_geofunc.cc:
  Usage of the Geometry class changed
sql/spatial.cc:
  Now we rewrite the real VMT of the object with new operation
sql/spatial.h:
  No need for the VMT-like structure and pointers to it
sql/sql_yacc.yy:
  enum items was renamed accordingly to coding standards