GeoExtPrintForm - print zone should follow drag

[adube]

Currently

While the GeoExtPrintForm widget is active, an orange box is displayed to demonstrate the print zone. After dragging the map, the box is adjusted to the map center. This is done using the map "moveend" event. This makes it difficult to perfectly adjust it exactly where we want.

Proposition

Make it follow the map "move" event so that it is always updated while dragging.

[adube]

There's a bug in OpenLayers which is only fixed in 2.12, so this ticket requires #460.

[adube]

(The bug appears when using map "move" event and dragging the map)

[adube]

Fixed in r1393.