vips_sequential() no longer bans all non-seq access, it just bans
rewinding --- if you ask for something some way ahead, it reads and
throws away pixels
this means VipsExtract and VipsInsert can now be seq: they will read and
throw away any stuff they don't need
cli operations turn on seq mode automatically when they can
vips_operation_get_flags() added: lets you attach a set of flags to an
operation
flags for now are "nocache" (replacing the old nocache system) and "seqential"
if vips_object_set_argument_from_string() from string sees "seq" flag on the
object for which it is setting the arg, it enables sequential mode
all operations which can run sequentially have been tagged
the operation printer knows about flags and can display them
Benjamin Gilbert
John Cupitt