Rewinding AnchorChanges makes the item's implicit width and height explicit

Problem: function void QDeclarativeAnchorChanges::rewind() in /src/declarative/util/qdeclarativestateoperations.cpp always calls setWidth() and setHeight() even when the AnchorChanges hasn't caused the width and/or height to become explicit.

See attached qml program as an example. When AnchorChanges is rewinded from a state, implicit Column height becomes explicit, breaking the implicit resizing behavior of the positioner. Seems fairly innocent, but the implicit resizing is important for many declarative elements, for example Rows, Column, Images, BorderImages and Text elements.

In the example a column contains 1 to 2 blue rectangle anchored to the bottom of the red rectangle with 10px margin. After the first state changes the column height stops following the number of rectangles it contains.