Program based of concept of hard linking of files being atomic across NFS.
This concept was mentioned in Mail::Box::Locker (which was originally
presented in Mail::Folder::Maildir). Some routine flow is taken from
there -- particularly the idea of creating a random local file, hard
linking a common file to the local file, and then checking the nlink
status. Some ideologies were not complete (uncache mechanism, shared
locking) and some coding was even incorrect (wrong stat index).
File::NFSLock was written to be light, generic, and fast.