Fixed Mac compilations targetting i386 and combined i386/x64

This updates the default target architecture to standard
(combined i386 and x86_64) and fixes compilation errors when
targetting i386. See:

http://stackoverflow.com/questions/7110245/error-building-32-bit-os-x-app

..for details on the compilation errors with synthesized properties
requiring explicit instance variables.
Merge pull request #1 from tommetge/master

Add universal architecture compatibility