Updates to code

Hey,

This adds support for iPad 2, as well as differentiating between iPhone 4 GSM and CDMA.
I also took the liberty of cleaning up the constant names a bit, and added macros to test for groups of devices instead of single devices (like "is this an iPhone 4" and "is this an iPad").

I'm not sure if this is something you want - but at least the 3 first commits should be interesting to you.

- Jørgen.