Closes #103. Loading contribs does not require slime-tests or ERT.

Tests are stored separately.

* Makefile (contrib-check-% check-%): Restore the check-<contrib>
target.
* .travis.yml (env): Use it.

* slime-tests.el (defun): Adapt to new contrib-tests location.
(readme-recipe, traditional-recipe): Don't use ert macros in
recipe tests, since ert might not be loaded.

* slime.el (slime-contrib-dependencies): New function.

* contrib/Makefile: Fix whitespace.
(check-%): Look for tests under /contrib/tests. Explicitly require
all needed test libs.

* contrib/inferior-slime.el: cleanup whitespace.

* contrib/slime-repl.el: Split off tests. Don't use `eval-and-compile'
* contrib/slime-presentations.el: Idem.
* contrib/slime-parse.el: Idem.
* contrib/slime-mdot-fu.el: Idem.
* contrib/slime-fontifying-fu.el: Idem.
* contrib/slime-enclosing-context.el: Idem.
* contrib/slime-c-p-c.el: Idem.
* contrib/slime-autodoc.el: Idem.

* test/slime-presentations-tests.el: New file.
* contrib/test/slime-parse-tests.el: New file.
* contrib/test/slime-mdot-fu-tests.el: New file.
* contrib/test/slime-fontifying-fu-tests.el: New file.
* contrib/test/slime-enclosing-context-tests.el: New file.
* contrib/test/slime-c-p-c-tests.el: New file.
* contrib/test/slime-autodoc-tests.el: New file.