Fix autodoc test failures on sbcl32 and cmucl

* .travis.yml (env): check less emacs 23 combinations. Pin tests
to sbcl32 for now.

* contrib/slime-autodoc.el (cerror "Foo"): test no longer fails for
sbcl.  (foo-inside-labels-2): test also fails on cmucl.

* contrib/ swank-arglists.lisp (print-decoded-arglist): for already
provided args, print strings literally.  (print-arg): New keyword arg
LITERAL-STRINGS