Added test DbManagerTests::EnumExecuteScalarTest(). Now test fails due to
errors in method DbManager.ExecuteScalar().
Changed behavior of method MappingSchema.ConvertChangeType(): if the
destination type is enum, we're using MapValueToEnum() method instead of
converting value to integer.
Merge branch 'pr/n232_darK-Zi0n-te4am-cr3vv'