Fix for bug #1253922 -- Quickview window is not staying on top of its parent in some *nix systems.
Fix QuickView windows not staying on top on some linux systems

Fixes #1253922 [quickview should be pinned on top of main GUI](https://bugs.launchpad.net/calibre/+bug/1253922)

Merge branch 'master' of https://github.com/cbhaley/calibre