Beginning to refactor document relationship links to reduce common code.

My attempts here are to mimic the `pagination()` method shared by
actions. I'm tentatively adding the `$count` property to actions so that
we can query the number of notices ''being displayed'' per page prior to
calling the actual `pagination()` method itself, since document
relationship `<link>` elements need to be output inside of `showHead()`,
before `showContent()`, which is where `pagination()` is, gets called.

lib/action.php

@@ -938,4 +938,38 @@ class Action extends HTMLOutputter // lawsuit
             $this->elementEnd('div');
         }
     }
+
+    /**
+     * Generate document metadata for sequential navigation
+     *
+     * @param boolean $have_before is there something before?
+     * @param boolean $have_after  is there something after?
+     * @param integer $page        current page
+     * @param string  $action      current action
+     * @param array   $args        rest of query arguments
+     *
+     * @return nothing
+     */
+    function sequenceRelationships($have_next, $have_previous, $page, $action, $args=null)
+    {
+        // Outputs machine-readable pagination in <link> elements.
+        // Pattern taken from $this->pagination() method.
+
+        // "next" is equivalent to "after"
+        if ($have_next) {
+            $pargs   = array('page' => $page-1);
+            $newargs = $args ? array_merge($args, $pargs) : $pargs;
+            $this->element('link', array('rel' => 'next',
+                                         'href' => common_local_url($action, $newargs),
+                                         'title' => _('Next')));
+        }
+        // "previous" is equivalent to "before"
+        if ($have_previous=true) { // FIXME
+            $pargs   = array('page' => $page+1);
+            $newargs = $args ? array_merge($args, $pargs) : $pargs;
+            $this->element('link', array('rel' => 'prev',
+                                         'href' => common_local_url($action, $newargs),
+                                         'title' => _('Previous')));
+        }
+    }
 }