vfs: add d_is_dir()

Add d_is_dir(dentry) helper which is analogous to S_ISDIR().

To avoid confusion, rename d_is_directory() to d_can_lookup().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>

diff --cc fs/namei.c
Simple merge

diff --cc include/linux/dcache.h
Simple merge