Wrapping the returned promises

[jakobmattsson]

Would it maybe be useful to add the possibility to wrap the promises returned from Z with another type of promises? Mixins only allow methods to be added/replaced, but the inner workings of the promises (like long stack traces etc) cannot be altered.

[jakobmattsson]

Create a case for this in the form of a test.

[jakobmattsson]

Using this, "complete resolving" could be implemented as such a wrapping (and hence optional) instead of being part of core.