support slightly more CLHS references

* contrib/slime-references.el (slime-references-properties): Support
`:type' and `:system-class' `:ansi-cl' references.
fix references to SBCL manual

I don't even want to think about how long it's been since SBCL switch
to an all-in-one-page manual format.

* slime-references.el (slime-lookup-reference-at-point): change format
for lookup in SBCL manual to match current all-in-one-page
publication.
Release 2.6
* swank-source-path-parser.lisp (make-source-recorder): Remove
FUNCTION type declaration, get-macro-character returns a
designator, not a function. Recent changes to SBCL exposed the
problem.
Implement FUNCTION-NAME, FIND-SOURCE-LOCATION for AllegroCL

Also, fix the docstring of DEFINTERFACE FIND-SOURCE-LOCATION.
Mention github workaround list in README.md
* swank-rpc.lisp (prin1-to-string-for-emacs): Convert floats into
double-floats, when possible. Emacs lisp only has double floats.
* slime-tests.el: Break long lines.
Fix display related bugs.

* slime-tests.el (display-region):  New test.
(slime-test--display-region-line-to-position)
(slime-test--display-region-eval-arg): New Helpers.

* slime.el (slime--display-region): Renamed from slime-recenter.
Also work in the case when the condition message takes up the
entire window.
(slime--adjust-window-start, slime--adjust-window-point): New
helpers.
(slime-show-source-location): Display buffer in other window, as
it always was.  Invert no-highlight-p argument to simplify
callers.  Add recenter-arg to get rid of the heuristic that
detected "sldb show source" vs. "show definition".
(slime--display-position): Factored out, again.
ChaneLog entry for last few changes.