Fix Paypal making requests using POST instead of GET.

[dhontecillas]

While I was testing using the Paypal sandbox I found I was getting POST request instead for GET for its notifications. I modified the code in a way that existing code won't break, but it will also handle the POST method.
Hope it gets merged.
Thanks.

[spookylukey]

This needs a unit test before it can be merged.

[dhontecillas]

I will try to put a test this weekend.

[dhontecillas]

I've enabled the PDT tests again in my fork. One of them is failing, and I guess should be fixed before I put tests for the POST method.
I've put the PAYPAL_IDENTITY_TOKEN in a separate file, to be sourced from bash (and on the runtests.py it reads it from the environment).

[spookylukey]

I had already re-enabled PDT tests in master, and done some fixes so that they all run and pass. From what I can see, the existing tests didn't need PAYPAL_IDENTITY_TOKEN to be a correct token.

It's not going to be practical for the test suite to depend on tokens that are not stored in the repo - it will severely hamper development if we have to depend on one particular person running the tests and reporting back to us.

[dhontecillas]

I've made a new pull request, with the fixes. Hope it is all ok.

[dhontecillas]

After messing it for a while yesterday night, I finally made the fix, and i've put the tests. It is in a new pull request. Shall I close this one?

[spookylukey]

Closed in favour of #68