Re-work $q a bit to better support decorators

[dcherman]

Currently, $q uses the defer() function in several places rather than referencing something like $q.defer()

This causes problems when you try to decorate promises because internally, $q is not calling the defer method that's defined/overriden in a decorator.

http://jsfiddle.net/3V2Xn/

[lgalfaso]

With 1.3 $q uses prototypes for promises, so this is already possible