Initialize the blueprint attribute in the __init__ method

The `init_app()` method may not have been called before methods
like `owns_endpoint()` is called which results in an AttributeError
being thrown.
error_router falls back on original when it fails

The flask-restful library was original designed to handle all errors that
happen within the domain of its restful endpoints.

This design decision collides with the assumption other library writers make,
trusting the custom error handlers they set up in the base app to kick in when
they throw one of their custom exception.

Given that flask-restful hijacks `app.handle_exception` on initialization,
that assumption of the latter developers causes some libraries to fail.

By making the flask-restful error_router fall back onto the `original_handler`
when the local one can't handle / re-raises the exception, we return the
control to the third-party extension handler for a last attempt at handling.

This is probably the case too for the `app.handle_user_exception` hijacking,
but it wasn't investigated this time around.
`usedevelop` flag in tox cuts run time by over half
Merge pull request #263 from jogura/fix_call_owns_endpoint_before_api_init

Initialize the blueprint attribute in the __init__ method
fix broken tests on py3.x due to #263
Improve RequestParser.copy method
simplify tests for parser.copy
Merge branch 'master' into error-router
dont catch EVERY exception
test to verify the error router falls back to the flask handler
Merge pull request #356 from flask-restful/error-router

Make error router fall back to flask error handler
Merge remote-tracking branch 'upstream/master'