branch changes from mitchel.jon

- Made changes to make the drag drop look more like the Windows 7 file
explorer drag drop.
- Displays the drag adorner all the time even when the DragDropEffect is
None.
- Offset the adorner so that the cursor is sat at the bottom middle of
the adornment.
- Added a DragDropEffect adorner object to allow the addition of a WPF
adornment for feedback instead of the standard monochrome cursor.
- Added dependency properties to allow the user to define their own
DragDropEffect adorners.
- Added default DragDropEffect adorners for the effect
None/Copy/Move/Link.
- Changed the events to tunnel instead of bubble.
- Improved drag effect adorner.
- Removed flicker from drag adorner.
- Added support for controls that inherit from TreeView. (might work
with other derived controls, but not tested)
- Added drop destination text to DropInfo for the effect adorner to
display.
- Fixed issue with cursor override not being reset on drop.
- A few updates to improve drag and drop for TreeViews.
- Added RelativeInsertPosition.TargetItemCenter enum so that the
DropInfo can tell the end user that the drop area is the middle 50% of
the target item.
- Marked assembly as CLSCompliant.