declared and installed IndeterminatesOfTuttePolynomial
declared and installed IndeterminateOfCharacteristicPolynomial
used IndeterminatesOfTuttePolynomial in RankGeneratingPolynomial
the methods for TuttePolynomial now work with two ring elements

these methods also set the attribute TuttePolynomial once
these two ring elements are *identical* with the standard
indeterminates returned by IndeterminatesOfTuttePolynomial( )
Merge pull request #3 from mohamed-barakat/master

the methods for TuttePolynomial now work with two ring elements