Fix consistency check.  The old test assumed that T could be added and
initialized by 0.
more unit tests
Introduce num_variables to phase out ambigious function name 'variables'
introduce num_vectors as a future replacement of ambiguous 'vectors'
rename get_result_variables to less ambiguous get_result_num_variables
Give GraverAPI its own compute function

This should be used for specialized GraverAlgorithms such as
ParallelGraver whose framework was also installed.