Add port comparison in __eq__() and __ne__() method to URL

Add port comparison in __eq__() and __ne__() method to URL

Comparing two objects of :class:`.URL` using ``__eq__()`` did not take port
number into consideration, two objects differing only by port number were
considered equal. Port comparison is now added in ``__eq__()`` method of
:class:`.URL`, objects differing by port number are now not equal.
Additionally, ``__ne__()`` was not implemented for :class:`.URL` which
caused unexpected result when ``!=`` was used in Python2, since there are no
implied relationships among the comparison operators in Python2.

Fixes: #4406
Closes: #4515
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4515
Pull-request-sha: 0f15b805f07e7fca1f82ca6c3aad98d50ea705b8

Change-Id: Iba7d224f1282dc3f4b884d1a746f2d46669f551e