Cache vCard retrieval.

We still need a cache invalidation mechanism. Currently PEP event notifications look most promising.
http://xmpp.org/extensions/xep-0163.html
http://xmpp.org/extensions/xep-0292.html#self-pubsub

converse.js

@@ -701,7 +701,6 @@
             $target.parent().remove();
             $('form.search-xmpp-contact').hide();
         }
-
     });
 
     xmppchat.RoomsPanel = Backbone.View.extend({
@@ -1363,7 +1362,19 @@
     });
 
     xmppchat.getVCard = function (jid, callback) {
-        // TODO: cache vcards
+        /* First we check if we don't already have a RosterItem, since it will
+         * contain all the vCard details.
+         */
+        var model = xmppchat.roster.getItem(jid);
+        if (model) {
+            callback(
+                model.get('jid'), 
+                model.get('fullname'), 
+                model.get('image'),
+                model.get('image_type'), 
+                model.get('url')
+            )
+        } else {
             xmppchat.connection.vcard.get($.proxy(function (iq) {
                 $vcard = $(iq).find('vCard');
                 var fullname = $vcard.find('FN').text(),
@@ -1373,6 +1384,7 @@
                 callback(jid, fullname, img, img_type, url);
             }, this), jid)
         }
+    }
 
     xmppchat.RosterItems = Backbone.Collection.extend({
         localStorage: new Backbone.LocalStorage("conversejs.rosterItems"),