Merge commit 'f4671f46e807db0e02d763e3a1685ad012eace5b' into 7.40
more doc additions
sync
exit() in fewer cases

we now only exit() when we know the stack has been trashed, just warn in
other cases
add "whole_slide" toggle

openslideload now crops to image bounds (if set) ... use @whole_slide to
stop this autocrop
change @whole_slide to @autocrop

on seconds thoughts, make openslide crop-on-load an option, not the
default

also, clip image bounds against image size
revise affine, yet again

how can this be so hard

the tougher self-tests in nip2/test/extras now all pass
Merge branch 'affine-bug'

Conflicts:
	libvips/resample/transform.c