Closes #105: Port indentation tests to use ERT

* contrib/test/slime-cl-indent-test.txt: Moved to from previous file and
changed test names from numbers to symbols.

* contrib/test/slime-indentation-tests.el: New file. Defines ERT
indentation tests from specs in `slime-cl-indent-test.txt'.

* contrib/slime-cl-indent.el: Moved tests to
test/slime-indentation-tests.el. In file comments, explain the
legacy cl-indent.el situation. Provide `slime-cl-indent'.

* contrib/slime-indentation.el (slime-cl-indet): `require' instead of
`load'.
Unhide presentation tests from batch test runs.

* contrib/test/slime-presentations-tests.el: Renamed from incorrectly
named test/slime-presentation-tests.el. Won't otherwise be run
from Travis CI.