[mythtv] Build slave failures

[Peter Bennett]

I see many build slave failures following the merge of MythUI settings.

Plugins - all fail building mythgallery. I believe mythgallery is now 
obsolete? Should it be removed from build? I can build plugins OK 
without mythgallery. It seems to be disabled by default in the configure.

jessie (incl rpi2) - build fails because vector removeAll is not found. 
That came with QT 5.4. Jessie has QT 5.3.2. I will work on getting rid 
of that incompatibility.

windows - ShowOkPopup': definition of dllimport function not allowed - I 
don't know what that means.

Peter