Merge branch 'master' of https://github.com/cbhaley/calibre
Update Countryfile.com
Fix text entry widgets' popup completion window not working well with windows on-screen keyboard. Fixes #1385586 [Autosuggest in text fields eats keystrokes from On-Screen Keyboard on Windows](https://bugs.launchpad.net/calibre/+bug/1385586)
Proper fix for closing completion popups when clicking on the drop down arrow of comboboxes that does not conflict with windows on-screen keyboard
Fix text in standard buttons not being translated because of a change in Qt 5.3
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Check Book: Silence incorrect warning about guide references to cover image in azw3 format
Fix #1385766 [Little typo](https://bugs.launchpad.net/calibre/+bug/1385766)
Fix #1385769 [Little typo?](https://bugs.launchpad.net/calibre/+bug/1385769)
Linux: Force use of GNOME button layout for dialogs when running under the GNOME, UNITY or MATE desktop environments
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Performance improvement: get proxy metadata once per book instead of once per user category