be more forgiving about x values

buildlut() would fail if rounding moved some of your x values away from
ints
fix vips_hist_match()

it wasn't upcasting input to uint due to a mix-up with VipsHistogram
Merge remote-tracking branch 'origin/7.36' into 7.36
fix some clang warnings
Merge remote-tracking branch 'origin/7.36'

Conflicts:
	ChangeLog
	configure.ac
	libvips/deprecated/im_exr2vips.c
	libvips/foreign/radiance.c