[gtkdatabox] gtkdatabox gtk+>=3.6 ready

[Johannes Deutsch <j_deutsch web de>]

Hi all,

i committed some changes to the `cairo-alpha` branch so that
`gtkdatabox` compiles with gtk+>=3.6.

I send a merge request over sourceforge.

Unfortunately the `cairo-alpha` branch had a detached head, so i'm  not
aware about what has changed so far.

It would be great if somebody could test the changes!?

Best regards