map elements are selected in IE when using shift key

[pgiraud]

Use case :

• Open the http://openlayers.org/dev/examples/vector-features.html example in your Internet Explorer browser,
• click down once on the text below the map,
• then press the shift key down, and click down on the vector polygon (or on a zoomBar element)
• elements are selected and are hilighted in blue

What happens is that the browser tries to select every thing between the first mousedown and the second.

Curiously, there is no problem if you click down anywhere else on the map.

It seems like a document.onselectstart overwrite is missing in the Drag Handler in the mousedown method.

Patch is attached

[pgiraud]

please review

[crschmidt]

Looks good, but needs a regression test.

[crschmidt]

(In [4230]) fix for 'map elements are selected in IE when using shift key' in drag handler from pierre. Confirmed that this can be tested simply by using anything with a drag handler in IE, so it will get caught in acceptance test. (Closes #792)