Move/delete file being written/read

[denismo]

Linux filesystems allow the files which are being written/read to be moved or even deleted without causing errors. This is probably because an open file creates a hidden hard link to the inode (not persisted) which keeps the inode up while the file name is removed.

We need to implement it in some way preferably without locking as I believe this mechanism is used by log rotators/archivers.