I wanted to get the bindings properly building with automake instead of
a raw Makefile in the src tree.  I also wanted the bindings to be a
reasonable python package so that so that workflow apps could just do

  import capnet.capnet as capnet

Well, doing all this with automake + setuptools is a bit of a problem
because we have to generate the python protobuf binding -- so our python
package source is split between the src and build dirs.  python's
setuptools doesn't really help us handle that at all.

But it *does* provide an escape hatch.  I can pull each package (or
subpackage) module from a different dir, so that's how this works.  We
pull the root package (capnet) from client/python/capnet ; then we pull
the capnet.proto package (which contains the generated binding) from
@builddir@/client/python/capnet/proto .

The python file import statements have all been updated to reflect this.