OverlayMask set opacity doest work on IE6 when the boundingBox is hidden, delay the setOpacity to when the boudingBox is visible;
OverlayMask set opacity doest work on IE6 when the boundingBox is hidden, delay the setOpacity to when the boudingBox is visible;

git-svn-id: eaac6977d0b6fa3343c402860739874625caf655@42243 05bdf26c-840f-0410-9ced-eb539d925f36

giros/alloy-ui,giros/alloy-ui,giros/alloy-ui,giros/alloy-ui