Added tests for VHDL unbounded arrays.

I had a problem with test_enumsystem again, so I marked it according to test results on my machine. I have seen that its status was updated to 'Passed' in the meantime, therefore it makes me wonder if there is anything wrong with my setup. I have tried to run the test with the current iverilog, but it has failed as well.
The new test (vhdl_unbounded) requires https://github.com/orsonmmz/iverilog/commits/unbounded_array to be merged.