Bug #133812 for File-NFSLock: share-mode locking bug

Hi. This could be characterized as misuse of the module, but I think there's a shared locking bug in NFSLock-1.29. Given the following: - two processes of different user - each process attempts to acquire a common lock file in shared mode The first process will successfully acquire the share mode lock. If a second process of a different user attempts to acquire the same lock, NFSLock will return success even though it has failed to append the lock file with the host and pid info. NFSLock::do_lock_shared calls create_magic ($self->{lock_file}) when the link fails (expected if the lock already exists). In create_magic, an undef is returned if the lock file can't be opened - as would happen if the lock file belongs to a different user. Although create_magic returns an undef, do_lock_shared doesn't check status from create_magic (the real bug here). This means do_lock_shared will return success even if the lock file was never appended with the new lock owner's info. Although this could be considered misuse, I think it would be simple enough to check the status from create_magic and fail the locking operation in do_lock_shared. Thanks Steven