With PyOxidizer 0.18.0 AppName in setup.py has to be changed to the
all lower case "linkchecker".
Application translations do not work.
better_exchook2.fallback_findfile() may still need converting, first
needs a test.
drop_privileges() is only used by the linkchecker command.
Move installing SIGUSR1 handler to the linkchecker command only - fixes
intermittent test failures.