BUG: Fix test_operand_flags test.

The test tests an inner loop in operand_flag_tests.c.src that expects
a long type, but it is tested using 'i8'. This fails when long is not
'i8'.

Closes #3363.
Merge pull request #3599 from charris/fix-operand-flags-test

BUG: Fix test_operand_flags test.