Oops, actually check attachment.
Better test.
Fix viewport scaling when not quantized.
Add --invert; fix scaling of non-quantized input.

When a --projection is specified, we assume that +y points down (as in SVG and
Canvas), and thus do not need to invert; however, then --projection is not
specified, we assume that +y points up (as in latitude).
Merge branch 'fix-filter-small-detached'