Added support for Gaussian priors on (transformed) model parameters (deactivated).

Fixed model sub-sampling issues with large objects, including check-image resizing.
Fixed initialization of DETMODEL size guess (thanks to Eli Rykoff).
Fixed image extension pb in double weighting/single image mode.
Improved debug info for memory allocations in FFT and FITS libraries.
Fixed crashes with DETMODEL magnitudes on null measurement weight maps.
Added Eli Rykoff's fix to discard sources with NaNs in the fitted positions.
Improved MKL autoconfiguration.
Improved vectorization in FITS data transformations and FFT-based convolutions.
Pushed SExtractor version number to 3.18.8.