'Return a modified copy of C{self} using C{newURL}, keeping the query
string if C{keepQuery} is C{True}.
@param newURL: a L{URL} to derive a new L{URLPath} from
@type newURL: L{URL}
@param keepQuery: if C{True}, preserve the query parameters from
C{self} on the new L{URLPath}; if C{False}, give the new L{URLPath}
no query parameters.
@type keepQuery: L{bool}
@return: a new L{URLPath}'

def _mod(self, newURL, keepQuery):

    return self._fromURL(newURL.replace(fragment=u'', query=(self._url.query if keepQuery else ())))
