Upgrade to newer log4j 1.2.x for munged library?

[apjanke]

Since our munged log4j 1.2.x won't be addressed by any other software, maybe no reason to stick on exactly 1.2.15. Maybe upgrade to a newer version in the 1.2.x series? Check their release notes and see if that's a good idea.

Log4Shell did not affect any 1.2.x; only 2.x, so that's not a concern here.

The log4j 1.2 series only has two more versions: 1.2.16 and 1.2.17. They're both bugfix releases. I don't see anything major, but might want to pick them up anyway by getting 1.2.17.

Loooot of bugfixes in 1.2.16. 1.2.16 makes those Sun Java jmx and jms JARs optional in the build. Might be convenient.

Make javamail, jmx, jms dependencies optional in pom.xml. Fixes 43304

Also "reasonable thread names".

Part of janklab/slf4m-jankalog#4.