Nothing earth-shattering, just a rewrite of the exact-aligner.scm oldie to fix some irritating problems: inability to work when there are several images open, and handling of some angles. At the usual place.

ofn-layer-aligner now has a sibling, ofn-layer-straightener, where you draw a path over what should becomes vertical/horizontal. It can also use two paths and average the result (for symmetrical objects that have no obvious vertical/horizontal lines).

Thanks Ofnuts for your useful scripts. Nice to have another one of yours.