Ensure dragged blocktype appears above view content area in IE (bug #891916)

In IE, when dragging a blocktype image into the content area of the
view editor, the image appears to slip underneath the white box saying
"This area shows a preview of what your page will look like..." and
then out the other side again.  Setting the z-index property on the
element containing blocktype list fixes the issue.

Change-Id: I6bc28bcf790b89d7513144012e210527b8ae1710
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>

htdocs/js/views.js

@@ -33,6 +33,10 @@ function ViewManager() {
             // base for positioned elements inside it
             self.columnContainer = $('column-container');
             makePositioned(self.columnContainer);
+            if (self.isIE7) {
+                // Stop blocktypes being dragged from disappearing underneath the content area
+                setStyle('top-pane', {'z-index': 1});
+            }
 
             // Hide 'new block here' buttons
             forEach(getElementsByTagAndClassName('div', 'add-button', self.bottomPane), function(i) {