David Johnson authored Sep 13, 2016 and Josh Kunz committed Sep 15, 2016

Mostly, this involves moving our controller's core MUL interaction
(i.e., all the module init and MUL callback stuff) into a separate file,
so we can build the core of controller.c into a lib that we can link
unit tests against.

In general, this whole thing is nasty, because libmulutil requires some
app callback stuff to be defined by whomever is implementing main(), and
of course everybody has to link against libmulutil.  In this case, since
the tests implement main(), we have to do a tiny bit of glue stubs.  The
amount of future glue code will depend on "unit test" paths into the MUL
code... we may have to grow a "test" version of mul_app_main.c, for
instance, or make that into a callable library.  Anyway, stuff for the
future.