Unbreak presentation functionality in inspector.

SWANK:*INSPECTEE-PARTS* has been gone for some time now, but
contrib/slime-presentations.lisp still used it to check object
availability in the inspector. Hid this logic behind existing
SWANK:INSPECTOR-NTH-PART, which behaves more like GETHASH.

* swank.lisp (inspector-nth-part): Don't break if index out of bounds,
return second FOUNDP value instead.

* contrib/swank-presentations.lisp (lookup-presented-object): No
longer reference *inspectee-parts* removed a long time ago.

* contrib/swank-presentations.el
(slime-menu-choices-for-presentation): slightly friendlier pop-up menu
title, could be friendlier maybe if object type were displayed
instead.
Make slime-repl tests less brittle.

The new tests don't assume that the REPL buffer has actual marker
objects indicating the relative positions of output, result and
prompt. This work is in preparation of handling issue #9.

* slime-repl.el (slime-repl-emit): Propertize the output text with
a `slime-repl-output' boolean property.
(slime-repl-test-markers): More powerful macro for testing repl text.
(slime-check-buffer-contents): Simplified with
`slime-repl-test-markers'.
(repl-test): tests with no output don't expect these markers.
(repl-type-ahead): tests with no output don't expect these
markers.
Fix slime-repl failures when run standalone

When run without slime-presentations, slime-repl exhibited some test
failures. This is a "sanity" fix so the current tests can be used as reference
for a possible redesign that eventually fixes #9 and maybe implements the
behaviour described in #84.

* .travis.yml (env): Test the slime-repl independently from other
contribs like slime-presentations.

* slime.el (slime-propertize-region): Add edebug spec.

* contrib/slime-repl.el (slime-repl-emit-result): Use
`insert-before-markers-and-inherit', and do it before saving `slime-output-end'.
(slime-repl-write-string): Fix failing tests by passing `eol' as t to
`slime-repl-emit-result'.
(slime-repl-test-markers): Friendlier test
assertions.