small fixes

help cleanup and debug if operations fail
more docs work
oop, affine coordinate error

we were offsetting the input image incorrectly, compare
the way the transform is set up in vips_affine_build() and
im__affinei()

see https://github.com/jcupitt/libvips/issues/131
forgot to turn off DEBUG
fix coordinate error in affine

see https://github.com/jcupitt/libvips/issues/131
fix affine in a better way

argh this time
Merge branch '7.38'

Conflicts:
	libvips/resample/affine.c
oops dropped a patch
update notes
small fixups

- remove -c abbrv. for --vips-concurrency
- better desc for insert
- revise vips.1 man page
doc fixups
better --vips-progress feedback for dzsave
Merge branch 'master' into load-from-stream
add a stream class