Fix recursive requester

[tikotzky]

Right now if you set a requester function in request.defaults it will override all further defined requester functions when using request.METHOD to make a request. For example

var request1 = request.defaults({}, function(uri, options, callback){
    console.log('I AM THE FIRST REQUESTER FUNCTION');
    request(uri, options, callback);
})

var request2 = request1.defaults({}, function(uri, options, callback){
    console.log('I AM THE SECOND REQUESTER FUNCTION');
    console.log('I WILL NEVER GET CALLED BY request2.METHOD');
    request1(uri, options, callback);
})

// currently using request.METHOD will only hit the first requester
request2.get(url)
// I AM THE FIRST REQUESTER FUNCTION

// using request directly will hit the both requesters
request({
  uri: url,
  method: 'GET'
})
// I AM THE SECOND REQUESTER FUNCTION
// I WILL NEVER GET CALLED BY request2.METHOD
// I AM THE FIRST REQUESTER FUNCTION

This PR fixes request.defaults so that recursive requester functions will get called by both request() and request.METHOD()

[nylen]

This is nice work, thank you for the PRs and for including tests 💚 I'll nominate it for $30 bounty if you're interested.

I'd rather see us use request instead of self / this, do you think that would cause any problems?

[simov]

t.deepEqual(r.request.headers, {foo: 'bar1'})

[tikotzky]

That is being asserted over here: https://github.com/tikotzky/request/blob/fix-recursive-requester/tests/test-defaults.js#L65

[tikotzky]

@nylen thanks for the offer of bounty nomination, but I'll pass on that for now.

As for changing to use request instead of this, are you referring to inside the request.METHOD function?

Changing that to use request instead of this would make it not use the requester function passed into request.defaults.

[nylen]

@tikotzky good point, 👍 from me then. I'll merge this tomorrow if no one objects or beats me to it.

@simov @tikotzky our test suite has come a long way 😬 and further patches are always welcome.

[tikotzky]

@nylen can this get merged now?