fix tab switching in Qt5

"QObject::connect: No such signal QTabBar::selected ( int )" is now
currentIndex(int)
http://qt-project.org/doc/qt-5.0/qtwidgets/qtabbar.html#currentIndex-prop
use type-checked QObject::connect wherever possible
version, changes
Merge pull request #23 from mvidner/typed-signals

fix tab switching in Qt5