Flask extension does not load configuration lazily

[youtux]

I am using raven[flask]==6.2.1 and it appears that the flask extension loads the configuration as soon as possible, rather than using lazy evaluation as Flask recommends.
This behavior results in no exception being forwarded to sentry, since my project needs to load the configuration after the application has been created.

I attach a snippet that replicates the issue.

import mock
import pytest

import flask
from raven.contrib.flask import Sentry

@mock.patch('raven.base.Client.send', autospect=True, return_value=None)
def test_lazy_configuration(m):
    app = flask.Flask(__name__)
    @app.route('/')
    def index():
        raise ValueError('Error here')

    app.sentry = Sentry(app)
    app.config['SENTRY_CONFIG'] = {
        'dsn': 'https://user:pass@whatever.com/44',
    }

    response = app.test_client().get('/')
    m.assert_called_once()