The following patch adds a syscall to the current linuxppc-2.5 tree.
This syscall allows in-application debuggers to work; it allows
debugging actions (currently setting the single-step bit and branch
trace enable bits) to be done for a setcontext, like a return from a
signal handler.

I have also attached a small program that demonstrates the usage of the
single stepping and branch tracing.

I'd like to get this into the standard kernel, but this is (obviously)
just for comment now.

-Corey