Refactor error code semantics

Bryan Forbese has created a branch which uses GError:
http://github.com/bryanforbes/libiphone/tree/gerror

Pro/Cons:
+ Allows error "bubbling/propagation" + Propagation might allow to normalize some error domains - Changes whole API ~ Further moves us to directly use glib overall (GObject, GError, etc.)

Feedback or other ideas welcome.

What I would make the decisive argument is how well one's implementation looks if it has to deal with errors.
With the current error system, implementations have to check for various error macros, one has to know the macro names and to make it hard we also have error domains to check (AFC_E_SUCCESS vs. NP_E_SUCCESS vs. LOCKDOWND_E_SUCCESS...).