Fix issue in old versions of IE with checkbox reading.

Some of the tests added in 4a22a5 apparently never worked in old IE. I added a capability check for the buggy behavior and a new path for IE.

Also, changed a `getAttribute` in a test to `readAttribute` — otherwise the test would never pass in IE 6-7, since `getAttribute` doesn't work right.

Author: savetheclocktower

src/prototype/dom/dom.js

@@ -2385,13 +2385,36 @@
     return element;
   }
 
+  // Test whether checkboxes work properly with `hasAttribute`.
+  var PROBLEMATIC_HAS_ATTRIBUTE_WITH_CHECKBOXES = (function () {
+    if (!HAS_EXTENDED_CREATE_ELEMENT_SYNTAX) {
+      // Only IE browsers are known to exhibit this one, so we'll take a
+      // shortcut.
+      return false;
+    }
+    var checkbox = document.createElement('<input type="checkbox">');
+    checkbox.checked = true;
+    var node = checkbox.getAttributeNode('checked');
+    var buggy = !node.specified;
+    return !node.specified;
+  })();
+  
   function hasAttribute(element, attribute) {
     attribute = ATTRIBUTE_TRANSLATIONS.has[attribute] || attribute;
     var node = $(element).getAttributeNode(attribute);
     return !!(node && node.specified);
   }
 
-  GLOBAL.Element.Methods.Simulated.hasAttribute = hasAttribute;
+  function hasAttribute_IE(element, attribute) {
+    if (attribute === 'checked') {
+      return element.checked;
+    }
+    return hasAttribute(element, attribute);
+  }
+  
+  GLOBAL.Element.Methods.Simulated.hasAttribute = 
+   PROBLEMATIC_HAS_ATTRIBUTE_WITH_CHECKBOXES ? 
+   hasAttribute_IE : hasAttribute;
 
   /** deprecated
    *  Element.classNames(@element) -> [String...]

test/unit/dom_test.js

@@ -1104,7 +1104,7 @@ new Test.Unit.Runner({
       checkedCheckbox = $('write_attribute_checked_checkbox');
     this.assert( checkbox.       writeAttribute('checked').             checked);
     this.assert( checkbox.       writeAttribute('checked').             hasAttribute('checked'));
-    this.assertEqual('checked', checkbox.writeAttribute('checked').getAttribute('checked'));
+    this.assertEqual('checked', checkbox.writeAttribute('checked').readAttribute('checked'));
     this.assert(!checkbox.       writeAttribute('checked').             hasAttribute('undefined'));
     this.assert( checkbox.       writeAttribute('checked', true).       checked);
     this.assert( checkbox.       writeAttribute('checked', true).       hasAttribute('checked'));