File checkout capability

[Larry Baum <lbaum@BOEING.COM>]

We are constantly running into the problem of two or more people editting
the same file simultaneously.  Of course, when we save our files the machine
does tell us that things are out of sync, but then we must reconcile our
changes.  

Does anyone have any code that implements some sort of "check-out" facility
so that we can be more aware of the fact that someone is already editting
a file (or even prevents simultaneous editting)?

Larry Baum