tests: perform an ast parse with Python 3 Previously, test-check-py3-compat.t parsed Python files with Python 2 and looked for known patterns that are incompatible with Python 3. Now that we have a mechanism for invoking Python 3 interpreters from tests, we can expand check-py3-compat.py and its corresponding .t test to perform an additional AST parse using Python 3. As the test output shows, we identify a number of new parse failures on Python 3. There are some redundant warnings for missing parentheses for the print function. Given the recent influx of patches around fixing these, the redundancy shouldn't last for too long.