OK, last message and i'll stop being a bother about this.

Matthias Scheler (the "maintainer" of the png package) was kind enough to
respond to a seperate message i sent him. Generally speaking answers to my
original questions are:

- If there's a problem with a package, open a PR (with "send-pr").
  (The MAINTAINER address (variable in the makefile) is not intended for
  use in bug reports.

- The problem i was seeing was caused by an out-of-date
  /usr/pkgsrc/mk/bsd.pkg.mk. 


 --johan