Bug 940387 - Australis customize mode: shouldn't be able to drag placeholders, r=jaws

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extra : rebase_source : 3334e9f310e0aaa14fda0325d3f74a0f05660b90
Bug 941372 - [Australis] ignore hidden elements for drag calculations, r=mikedeboer

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extra : rebase_source : 584eacdc6035d34abeb6eed4ed622cbb80f6e85c