`setAttribute` doesn't correctly change checked state.

If the user changes the checked state of a checkbox input, `setAttribute`
will stop updating the UI. It appears that internally the state is set
but the interface doesn't match.

Fix is to use a more thorough approach for the checked case, somewhat like
`getInputValue` already does.

@@ -151,10 +151,17 @@
 
   attributeBinding = function(attr) {
     return function(el, value) {
-      if (value) {
-        return el.setAttribute(attr, value);
-      } else {
-        return el.removeAttribute(attr);
+      switch (attr) {
+        case 'checked':
+          el.setAttribute('checked', value);
+          el.checked = value;
+          return el.defaultChecked = value;
+        default:
+          if (value) {
+            return el.setAttribute(attr, value);
+          } else {
+            return el.removeAttribute(attr);
+          }
       }
     };
   };

@@ -86,7 +86,16 @@ getInputValue = (el) ->
 # Returns an attribute binding routine for the specified attribute. This is what
 # `registerBinding` falls back to when there is no routine for the binding type.
 attributeBinding = (attr) -> (el, value) ->
-  if value then el.setAttribute attr, value else el.removeAttribute attr
+  switch attr
+    when 'checked'
+      el.setAttribute( 'checked', value )
+      el.checked = value
+      el.defaultChecked = value
+    else
+      if value
+        el.setAttribute attr, value
+      else
+        el.removeAttribute attr
 
 # Returns a state binding routine for the specified attribute. Can optionally be
 # negatively evaluated. This is used to build a lot of the core state binding