Give global properties reference symmantics

Linking properties with the global properties concept should act as if the 
linked property is just a reference to the global property. This means that 
changing the value of the linked property will also change the value of the 
global property. It has to be made sure that changes don't cascade if the value 
of a property is practically unchanged. This means that changes shouldn't 
trigger anything unless it is a true change. Automatic triggers are also 
discouraged.

Original issue reported on code.google.com by brosch....@gmail.com on 26 Apr 2013 at 6:42

e-thereal / gapputils

Give global properties reference symmantics #74