Multiple Different Implementations of isPromiseLike()

[aebabis]

promises-aplus-test-adapter uses the following code to determine if an object is promise-like:

var isPromiseLike = function isPromiseLike(obj) {return obj && isFunction(obj.then);};

ngAnimate does this:

var isPromiseLike = function(p) {
    return p && p.then ? true : false;
};

and Angular.js does this:

function isPromiseLike(obj) {
    return obj && isFunction(obj.then);
}

Perhaps they should all be changed to this:

function isPromiseLike(obj) {
    return obj && typeof obj.then === 'function';
}

[jbedard]

There's also another stricter version in $q

[aebabis]

@jbedard Perhaps $q should expose this functionality for other apps to use.

[lgalfaso]

The version at promises-aplus-test-adapter should probably be removed as $q does not use it. I think it is not easy to expose isPromiseLike inside $q and make $q use that implementation without making the code slightly weird, but if someone wants to give it a shoot, then I can review the PR