'Give all changes between file1 and either file0 or file2.'

def pair_changes(self, fromindex, toindex, texts):

    if (fromindex == 1):
        seq = (toindex / 2)
        for c in self.all_changes(texts):
            if c[seq]:
                (yield c[seq])
    else:
        seq = (fromindex / 2)
        for c in self.all_changes(texts):
            if c[seq]:
                (yield self.reverse(c[seq]))
