Fixed issue with MINIBACKGROUND and MINIBACK_RMS multi-extension check-images.

Added new measurement parameters:
FLUXRATIO_POINTSOURCE :    Point-source flux-to-total ratio from fitting,
FLUXRATIOERR_POINTSOURCE : Uncertainty on point-source flux-to-total ratio,
FLUXRATIO_SPHEROID :       Spheroid flux-to-total ratio from fitting,
FLUXRATIOERR_SPHEROID :    Uncertainty on spheroid flux-to-total ratio,
FLUXRATIO_DISK :           Disk flux-to-total ratio from fitting, and
FLUXRATIOERR_DISK :        Uncertainty on disk flux-to-total ratio.
Pushed version number to 2.19.0