Have makefile_new() obey o->output_path

I guess I'd never tested for this before.  At least it's easy to fix!
Implement "--binname" and "--srcname"

This allows a structured way for scripts to query pconfigure as to
what the resulting object name will be when a particular source
(inside a given binary) ends up being compiled.

I should probably add support for something like --libname, but I'm a
lazy bum.