Due to a defect in the precise spatial operation algorithm design 
and implementation ST_CONTAINS()/ST_WITHIN wrongly report that a polygon 
doesn't contain itself. Also ST_EQUALS() wrongly returns 0 for the same 
polygons with shifted vertices.
Fixed by:
1. making ST_EQUALS() to ignore vertices shifting and
2. checking arguments equality at the very beginning
of the ST_CONTAINS()/ST_WITHIN().