Message 50048 - Python tracker

The "itch" that is scratched by this patch is the wish to be able to use a 
python binary that was build on OSX 10.4 on OSX 10.3 systems. At the 
same time the binary should offer full access to OSX 10.4 API's when 
running on that system.

This patch weakly links a number of functions in the posix, time and 
socket modules.

I'm not quite happy with code duplication in the time and socket modules, 
but don't quite know how to fix that.