the new sequential mode readers for tiff/jpg/png were not working well
from the vips7 command-line: they either decompressed twice, or handed
over a sequential mode image
it should now work as well as it did pre-seq.
the vips7 loaders were a thin layer over the new VipsForeign system
however! VipsForeign does various "useful" things, like open via disc,
and this resulted in stuff like
vips im_jpeg2vips huge.jpg x.v
decompressing to a temp file before copying to x.v
im_jpeg2vips() and friends now call the low-level loaders directly and
avoid the extra mechanisms in VipsForeign
"nip2 huge.jpg" was loading twice as well, for the same reason
John Cupitt