Use sys.executable to get script directory when frozen.

py2exe overwrites sys.path[0], and the paths to the registration
helpers end up wrong. If we are frozen, use dirname(sys.executable)
instead of sys.path[0].
Use py2exe in dist-exe target.

Make the dist-exe make target use p2exe rather than pyinstaller.
This removes some error handling and cleanup.
Change bundling instructions to work with py2exe.

py2exe requires extra work to help it find modules, like unzipping
eggs and creating dummy __init__.py files.