Jack Lin reports that the error return from dup3() for the RLIMIT_NOFILE
case changed incorrectly after 3.6.

The culprit is commit f33ff992 ("take rlimit check to callers of
expand_files()") which when it moved the "return -EMFILE" out to the
caller, didn't notice that the dup3() had special code to turn the
EMFILE return into EBADF.

The replace_fd() helper that got added later then inherited the bug too.
Reported-by: NJack Lin <linliangjie@huawei.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
[ Noted more bugs, wrote proper changelog, fixed up typos - Linus ]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>