Integrate tests with make check

[phst]

We probably want to run the tests in make check. The test modules should also automatically be recompiled whenever Emacs changes (i.e., they should use a normal subdir Makefile instead of modhelp.py). While there, I think we should merge the existing test modules into one: multiple test modules add some clutter and don't buy us much.

[aaptel]

We can do this "properly": make each (well maybe just one if we merge all tests) makefile go through autoconf to make it work on all supported platform.

Or "hide it under the carpet" for now and basically just move the modules/ dir into the test dir, and simply making the Makefile file call modhelp.py. This might be a good first step.