Enable escl backend in Ubuntu-16.04
If these two functions jpeg_skip_scanlines
and jpeg_crop_scanline
are not found, image cropping is disabled.
escl does not support X and Y.
OPT_TL_X and OPT_TL_Y used with jpeg_crop_scanline and jpeg_skip_scanlines emulates it.
!370 (closed) allows to use the escl backend with OPT_TL_X=x_range.min and OPT_TL_Y=y_range.min and does not use jpeg_crop_scanline and jpeg_skip_scanlines.
OPT_TL_X and OPT_TL_Y are no longer modifiable.
escl can be activated even with an old version of libjpeg!
Edited by ThierryFR