Sanitize URL for services

[tomkralidis]

As reported in Ref: cga-harvard/Hypermap-Registry#242, when OWSLib initializes OWS class instances the usual behaviour is to internally build a full GetCapabilities request via HTTP GET. We need to ensure that URLs passed with the basic service elements (service, version, request) are stripped of these elements so they are not passed twice when OWSLib interacts with the OWS.

Examples:

>>> from owslib.csw import CatalogueServiceWeb as csw
>>> c = csw('http://demo.pycsw.org/cite/csw')
>>> c.request
'http://demo.pycsw.org/cite/csw?version=2.0.2&request=GetCapabilities&service=CSW'
>>> c = csw('http://demo.pycsw.org/cite/csw?service=CSW&version=2.0.2&request=GetCapabilitiesd')
>>> c.request
'http://demo.pycsw.org/cite/csw?service=CSW&version=2.0.2&request=GetCapabilitiesd&version=2.0.2&request=GetCapabilities&service=CSW'
>>> from owslib.wms import WebMapService as wms
>>> w = wms('http://tepeserwery.pl/tileservice/wms.php/icrsptixwh?SERVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities')
>>> w.request
'http://tepeserwery.pl/tileservice/wms.php/icrsptixwh?SERVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities&service=WMS&request=GetCapabilities&version=1.1.1'

[tomkralidis]

Fixed in #375