Create a partial pid file already in the start script, to minimize races.
Also use the pid file to avoid starting duplicate servers in the start
Compatibility note: The start script now always has a fallback for the pid
file setting, to make the detection mentioned above effective. That renders
the pid file setting in Global Variables ineffective, and it has therefore
been removed. Installations which it therefore need to move it to the start
script command line, or the ROXEN_PID_FILE environment variable.