Forward port 2.x code quality improvements to 3.x

[rdmark]

There are a handful of minor improvements that were made in 2.x that should be ported to 3.x, e.g. this commit bda8274

Examples include safety checks in afppasswd.c

[rdmark]

I was able to port most relevant patches cleanly in #952

Two patches I'm holding back for now because they don't apply cleanly to main, and some deeper reading is required to make sure there are no side effects:

34c6c30
9a75cb8

[rdmark]

The former now done with #1023

The latter is just cleanup of unused variables. That can be done at a later time for the codebase as a whole.