remove the wrong comment at: class ret<Holder_T, T, 0>
use explicit convert to avoid compile warning
remove test_orm_bulk() and test_convert() from common-tests.h to test-oracle.cpp.

I saw some assert failed at travis-ci. because I was tested in Oracle database, so I just move it to test-oracle.cpp and try to pass all test
remove test_orm_bulk() and test_convert() from common-tests.h to test-oracle.cpp.

I saw some assert failed at travis-ci. because I was tested in Oracle database, so I just move it to test-oracle.cpp and try to pass all test
change static T return_value(const Holder_T& h) -> static T return_value(const Holder_T& ) to avoid compile warning
remove test_orm_bulk() and test_convert() from common-tests.h to test-oracle.cpp.

I saw some assert failed at travis-ci. because I was tested in Oracle database, so I just move it to test-oracle.cpp and try to pass all test