Fix fn.closest() on collections of multiple elements

The lookup needs to start on all elements of the collection
simultaneously and eliminate duplicated results as it traverses up the
DOM tree. Previously, the lookup only started at the 1st element of the
collection.

Fixes #1104

src/zepto.js

@@ -515,11 +515,13 @@ var Zepto = (function() {
       return result
     },
     closest: function(selector, context){
-      var node = this[0], collection = false
-      if (typeof selector == 'object') collection = $(selector)
-      while (node && !(collection ? collection.indexOf(node) >= 0 : zepto.matches(node, selector)))
-        node = node !== context && !isDocument(node) && node.parentNode
-      return $(node)
+      var nodes = [], collection = typeof selector == 'object' && $(selector)
+      this.each(function(_, node){
+        while (node && !(collection ? collection.indexOf(node) >= 0 : zepto.matches(node, selector)))
+          node = node !== context && !isDocument(node) && node.parentNode
+        if (node && nodes.indexOf(node) < 0) nodes.push(node)
+      })
+      return $(nodes)
     },
     parents: function(selector){
       var ancestors = [], nodes = this

test/zepto.html

@@ -1176,6 +1176,13 @@ <h1>Zepto Core unit tests</h1>
         t.assertLength(0, el.closest('form'))
       },
 
+      testClosestMultiple: function(t){
+        var els = $('#parents ul li')
+        var uls = els.closest('ul')
+        t.assertEqualCollection($('#parents ul'), uls)
+        t.assertEqualCollection($('#parents'), uls.closest('#parents'))
+      },
+
       testClosestWithCollection: function(t){
         var targets = $('#parents > li')
         var result = $('#li2').closest(targets)