[Merge] lp:~jamesh/gallery-app/thumbnail-mtime into lp:gallery-app

[James Henstridge]

I think I've got this working now.  I've added a refresh() call that clears the cache of the QFileInfo embedded in the MediaSource object, and called it prior to emitting the signal.
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https://code.launchpad.net/~jamesh/gallery-app/thumbnail-mtime/+merge/268185
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