Remove (int) file descriptor locking. It should be up to the
application to provide locking for I/O operations. This doesn't
break any of my tests, but the old behavior can be restored by
compiling with _FDLOCKS_ENABLED. This will eventually be removed
when it is obvious it does not cause any problems.

Remove most of flockfile implementation, with the exception of
flockfile_debug.

Make error messages more informational (submitted by Mike Heffner
<spock@techfour.net>, who's now known as mikeh@FreeBSD.org).