Well, apparently the -x parameter to bash simply means that it will output all script lines to stdout, and that causes the slightly slower execution.
I'm thinking about instead adding the -t parameter to the killproc command (on lines 103 and 109).
I attached my own init script, which handles shutdowns quite gracefully. Actually, your system will fail to shut down at all if slapd remains running.
(Looking at this code now, well, I honestly don't remember writing at least parts of it, so I can't take credit for it.)
HTH
John