- On OSX add -no-cpp-precomp to OPT. The user still has to manually specify

- On OSX add -no-cpp-precomp to OPT. The user still has to manually specify
  the --with-suffix=.exe, but it seems that that is also true for cygwin
  (or not? should I automatically set it?)
- Got --with-next-framework to build on OSX. This is only the build bit,
  the install still has to be done manually. Moreover, the Python build order
  isn't really suited to frameworks (where you want to do 'build lib',
  'install lib and framework', 'link executable against installed framework'
  in that order).