[patch] [cla] ComboBox fires onChange when leaving the ComboBox

[wolfram]

A side effect occured when fixing #4617, when leaving the ComboBox? (bluring, just clicking outisde of it) the onChange event was fired, due to setDisplayedValue() being called here /browser/dijit/trunk/form/ComboBox.js#L405, this patch fixes it, simply leave the displayed value as it is, since the value for setting it was previously retreived by getDisplayedValue() it seems invain anyway. I tested the use case described in #4617 and it still works.