This patch fixes some problems with linux/ppc callbacks. Some of the
callback tests will still fail but they are due to other problems with
linux/ppc. These are that you can't currently pass more than 8 floats
in a C call, nor can you pass long longs.
Without the patch, callbacks on linux/ppc trash the stack in most
cases. The qsort callback test fails to complete for this reason.
With the patch it works properly.
Please apply or let me know what else should be done first.
I'll put in a seperate patch to test the other bugs and/or fix.