Use the ".so" suffix for the readline completer on macOS

It used ".dylib" for the readline completer module, but since this
is our extension, we need to use ".so".

doc/HTML/stklos-ref.html

@@ -14538,7 +14538,7 @@ <h4 id="_system_information">4.13.5. System Information</h4>
 </div>
 <div class="listingblock">
 <div class="content">
-<pre class="rouge highlight"><code data-lang="scheme"><span class="p">(</span><span class="nf">features</span><span class="p">)</span> <span class="nv">=&gt;</span> <span class="p">(</span><span class="nf">STklos</span> <span class="nv">STklos-2</span><span class="o">.</span><span class="mf">00.1533</span> <span class="nv">exact-complex</span>
+<pre class="rouge highlight"><code data-lang="scheme"><span class="p">(</span><span class="nf">features</span><span class="p">)</span> <span class="nv">=&gt;</span> <span class="p">(</span><span class="nf">STklos</span> <span class="nv">STklos-2</span><span class="o">.</span><span class="mf">00.1534</span> <span class="nv">exact-complex</span>
                <span class="nv">ieee-float</span> <span class="nv">full-unicode</span> <span class="nv">ratios</span> <span class="nv">little-endian</span> <span class="o">...</span><span class="p">)</span></code></pre>
 </div>
 </div>
@@ -31446,7 +31446,7 @@ <h3 id="_addendum_how_to_use_this_license_for_your_documents">B.13. ADDENDUM: Ho
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2023-09-11 17:32:28 +0200
+Last updated 2023-09-11 17:46:01 +0200
 </div>
 </div>
 </body>

lib/readline.stk

@@ -175,9 +175,10 @@
 
 (define (try-initialize-readline)
   ;; Try in sequence the GNU readline and BSD libedit (which has readline support)
-  (let* ((suffix (%shared-library-suffix))
-         (res (or (try-initialize (string-append "libreadline." suffix))
-                  (try-initialize (string-append "libedit."  suffix)))))
+  (let* ((lsuffix (%shared-library-suffix))
+         (suffix  (%shared-suffix))
+         (res (or (try-initialize (string-append "libreadline." lsuffix))
+                  (try-initialize (string-append "libedit." lsuffix)))))
     (when (and res (try-load (string-append "readline-complete." suffix)))
       ;; We have found a readline library. Try to load completion support
       (%init-readline-completion-function readline-completion-generator))