Add "normalizeProgramPath" to WLP.ProgramPath

Some functions seem to assume that the program paths are formed by a
fully left-associative application of the Seq constructor (as in: Seq
Skip $ Seq Skip $ ... $ Seq Skip Skip). Therefore, this function is
added; it will turn any string of Seq'ed statements into this shape.
Using this function will do no harm (other than possibly spending effort
into doing nothing), so use it accordingly.