Show filename and line in syslog only when the level _is_ debug

… instead of only when it _isn't_.  The commit which introduced logging
to syslog, b5956dc, had this backwards from the start.
Log the process id at the beginning of each log line

This helps differentiate multiple web server processes when untangling
logs.  It's very useful for tracing mail flow more quickly.
Merge branch '4.0/standard-log-message-tweaks' into 4.0-trunk