In MachoPython, don't simulate argc/argv unless we have argc=1 and argv[1]

In MachoPython, don't simulate argc/argv unless we have argc=1 and argv[1]
starts with "-psn_". This means the drag-and-drop continues to work as
expected, but we can now also do
/Applications/Python.app/Contents/MacOS/python script.py
from the command line, which is a lot easier with debugging. Pressing <option>
at this point also has the expected effect of opening the options dialog!