[IE] Backspace button on control type trigger history backward

[garry.yao]

This's a migration of #327.

Reproducing Procedures

1. Open the 'replace by class' sample page;
2. Insert a control type( e.g. Image, form control, table ) and select it;
3. Press 'Backspace';
   • Actual Result: Browser history backward is triggered.
   • Expected Result: The control is deleted from document.

[tobiasz.cudnik]

I think it's proper place for this fix. Only one thing worries me - double saveSnapshot event. I think it won't create redundant image, but it's because editor is not taking snapshot at start.

[garry.yao]

Don't worry, there're no duplicate snapshots, since the default 'keydown' event ( which trigger the undo system ) has been canceled, though there were some issues with the previous patch, I'm pasting a new patch:

1. The fix should be scoped to any control type element;
2. Please use the standard way to cancel event;

[homestar9]

For some reason the fix does't work for me in IE7. Patch applied but behavior is the same.

[fredck]

Good one... on commit, just to make it a bit smaller and mainly more readable:

var control = event.data.keyCode == 8 && editor.getSelection().getSelectedElement();
if ( control )

[garry.yao]

Fixed with [4347].