Can I help with something to make this PR move forward?

LGTM

Why this feature was introduced as patch for Angular 1.3.x? I think it is a breaking change and should be introduced in Angular 1.4.x. because many developers use 0 instead of -1. proof.

@dizel3d - thanks for getting in touch. The status of an error was not defined as a public API in the Angular docs. The reason we used to (incorrectly) return 0 for all errors was that browsers were inconsistent in their error return values.
What we guarantee, which has not changed, is that successful requests would return a value between 200 and 299, inclusive.
To tell if a request errored, you should really be using an error handler via then(successFn, errorFn). What this added was a way of telling if the error was because of a timeout.
If you must use the status to check for an error, then perhaps you should test for <=0 rather than ==0.