This variation on fcntl() record-locks resolves multiple-thread / forking
issue with region locks. No longer falls back to using flock() (whole-file
locks), when OFD locks are available and used successfully. At the least,
this should provide a performance boost for shared files using region
locks (on Linux). No change for Windows (region locks already worked sanely
among multiple threads) and other *nixes (that use POSIX fcntl() locks
only).