The requirements on a freezing tool to work with the freeze support in the multiprocessing library are unclear.

In particular, I'm trying to support multiprocessing in py2app and cannot rely on the documentation to implement that support.

The particular issue I run into:
- With py2app "sys.executable" points to a regular interpreter
- py2app sets sys.frozen to "macosx_app" or "macosx_plugin"
- Multiprocessing.spawn.get_command_line() assumes that a special command-line should be used when "sys.frozen" is set and there is no way to disable this.

The easiest way for me to fix this issue is to drop setting sys.frozen in py2app, although I have no idea what other code this might break.