This patch updates to netpbm to the latest tag in its release series
("advanced"), 10.78.3.

I tested that all the packages that refer to netpbm still build. The
main dependent package is groff.

There are two new test failures that I don't understand yet. Here is the
output of those two tests, run with `set -x`.

There are many security issues fixed since the netpbm package was
created; I don't have a tally. Some of these fixes are contained in this
release, but some are only available on the netpbm 'super-stable'
branch. The netpbm release strategy is complicated; it will take some
time to find relevant bug fixes and port them to this release series.

Your thoughts?