Bug 901360 - (Part 1) Use Downloads.jsm for download notifications. r=wesj

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extra : rebase_source : a05527361fcde5d7fd7b77b3bcc46955750d19e2
Bug 901360 - (Part 2) Fix PDF downloads. r=margaret

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extra : rebase_source : c0b856edd344292fc28384e18e1474cb7198b28a
Bug 901360 - (Part 3) Persist download history forever. r=paolo

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extra : rebase_source : 694428b676809cf0a0c10a81d68e02183d11f780
Bug 901360 - (Part 4) Fix clicking on notifications. r=margaret

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extra : rebase_source : 6bac7cd282d7ec795d91c0dbb685027890d6e840
Bug 901360 - (Part 5) Don't allow pausing downloads without partial data. r=margaret

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extra : rebase_source : c5455e3d650711692af3f97d90dd002845dcc669