Update version to 3.1.3.
[mac] bump version to 3.1.3
Merge pull request #167 from Chilledheart/release-3.1.3

[mac] bump version to 3.1.3
added @2x icons
remove debug output
added more 2x icons
[mac] cmake support for osx bundle build now

 - remove os x bundle functionity from qmake
 - introduce some changes of osx bundle's directory layout
 - 1st attempt to migrate genapp.sh into cmake script
[cleanup] cleanup compiler warning
[mac] revert 3a186da since it is fixed in qt upstream

  - report is availabe at QTBUG
    https://bugreports.qt-project.org/browse/QTBUG-10899
  - eliminate compiler warning about deprecated usage of objc_class
use type double instead of float for scalefactor
[mac] enable retina mode as default
[mac] fix build issue under osx 10.6