Changes related to rectangular detectors

  - many fixes to properly handle rectangular detectors;
    much of the code, while accepting different input values for
    the number of rows and columns on the detector, was
    either hard-coded or sloppily coded for the case of a
    square panel.  These changes are incremental; we still need to
    address the case of non-uniform r/c pixels size (admittely
    a rare case).  Much of the final cleanup will happen as a
    result of the reader/detector refactor.  For now, the
    find-orientations and fit-grains have been verified using
    a gold test case from Ulrich Lienert.