clplumbing: Bug 1454 - Detect stale PID files where possible
Linux-only patch from Kevin Jamieson, cleaned up and made usable on other
systems by Andrew Beekhof.
All systems heck for a running PID, Linux systems supporting /proc/{pid}
additionally checks that it has not been reused.

--HG--
extra : convert_revision : c62afda08611313b1a2cfea6a7382ba6dea9b928