Documenting RENAME_WHITEOUT

Hi Miklos,

I just noticed that your RENAME_WHITEOUT flag went into Linux 3.18:
commit 0d7a855526dd672e114aff2ac22b60fc6f155b08
commit 787fb6bc9682ec7c05fb5d9561b57100fbc1cc41

Would you be willing to write some text for the rename(2)/renameat2(2)
man page that described this flag. In that text it would be great to
have an explanation of what a whiteout is and why they are useful.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/