[tiff] fix output as RGB when PLAIN was intended.
[tiff] fix output as RGB when PLAIN was intended.

  - I think the error reporting in Gene's library is a little messed up.
    It was giving me a "orientation" tag not found error, which threw me
    off for a bit.  The real error, found be stepping through the code,
    was having not enough samples-per-pixel for an rgb image; the
    photometric interpretation tag was off.  It sends an error string to
    that effect, but it isn't properly recorded...I think Grab_Message_8qm5()
    returned false when it shouldn't have.

TeravoxelTwoPhotonTomography/nd,TeravoxelTwoPhotonTomography/nd