The known bug (bogus error message when an empty file is
extracted) is fixed.

Other changes:

- The target-compile and target-optimize flags of bdist_wininst
  are gone. It is no longer possible to compile the python
  files during installation.
- The zlib module is no longer required or used by bdist_wininst.

- I moved the decompression/extraction code into a separate
  file (extract.c).

- The installer stub is now compressed by UPX (see
  http://upx.tsx.org/). This reduces the size of the exe
  (and thus the overhead of the final installer program)
  from 40 kB to 16 kB.

- The installer displays a more uptodate user wizard-like
  user interface, also containing a graphic: Just's Python Powered logo.
  (I could not convince myself to use one of the BeOpen logos).
- The installation progress bar now moves correctly.