MFC 232401:

MFC 232401:
Similar to the fixes in 226967 and 226987, purge any name cache entries
associated with the previous vnode (if any) associated with the target of
a rename().  Otherwise, a lookup of the target pathname concurrent with a
rename() could re-add a name cache entry after the namei(RENAME) lookup
in kern_renameat() had purged the target pathname.

git-svn-id: svn://svn.freebsd.org/base/stable/8@233386 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f