test: emacs: run list-processes after accept-process-output in emacs 23.1

When running emacs tests using emacs 23.1.1 the tests block (until timeout)
when emacs function (notmuch-test-wait) is called.

There is an emacs bug #2930 titled:
23.0.92; `accept-process-output' and `sleep-for' do not run sentinel

It seems this is present in emacs 23.1.

Calling list-processes after accept-process-output seems work around
this problem; in case Emacs version is 23.1 a defadvice is activated
to do just that.