Improve handling of errors returned by bitbucket.

[mikerussellnz]

When creating a pull request via PullRequests.Create if the specified from branch / to branch is not found, bitbucket will return 404 not found. But the contents of the response will be a JSON structure that explains what was not found.

The issue is this JSON response is never read if the HTTP status code is 404.

The exception thrown is:
POST operation unsuccessful. Got HTTP status code 404.

I have modified a local checkout of the code to add reading the response data, which provides me the JSON error details as text in the exception:

Modified code - HttpCommunicationWorker, Line 97:

                string error = await httpResponse.Content.ReadAsStringAsync().ConfigureAwait(false);
                throw new Exception(string.Format("POST operation unsuccessful. Got HTTP status code '{0}' \nContent:\n{1}", httpResponse.StatusCode, error));

This is not ideal as it would be nice to deserialize the JSON error response to some sort of class structure.

Thanks.