I just confirmed both--thank you so much! We truly appreciate your help.
I followed the instructions at SourceForge's VHOSTs page (https://sourceforge.net/p/forge/documentation/Custom%20VHOSTs/), but it didn't make a difference. The SF png-mng project admin page explicitly says "Your VHOST domains will not work with HTTPS" despite the lack of any such statement on the Custom VHOSTs page, and that seemed to be confirmed by one of my browsers' error pages on loading (something about ...sourceforge... domain on the certificate not matching libpng.org).
Adding report with -v option below : $ ls 1.c 2.c $ zip -rv ../test1.zip . adding:...
Fix comma-related configure breakage.
Fix off-by-one IndexedLineSet bug; add missing ...
Fix several snapshot-indexing bugs, and replace...