correct linking between tests.
fix calculation of N flag.
fix setting of Z flag.
fix bugs in calculation or operand address.
ORA doesn't expect data result to change.
add shortcut for expecting results to match inputs.
correctly initialise expected results from test.
calculate expected value of Z flag correctly.
remove debug output.
factor out looping through test cases for reuse.
add benchmarking program for convenience.
use test_next_alu to select next test.