No more temp files in data or data/temp.
ctrl_dir/../temp (e.g. sbbs/temp) is the new default temp dir.
Each server has its own separately configurable temp dir.
BBS events (e.g. QWK packet processing) now have their own exclusive-use
temp dir (e.g. sbbs/temp/event).
All server threads will attempt to create and verify the validity of their temp dir.
System temp dir is only the default global temp dir for Unix (i.e. /tmp), since
the Windows default temp dir (e.g. C:\DOCUME~1\Rob\LOCALS~1\Temp) is not
particularly friendly or attractive.