Sanitize exec_permission_lite()

Use the sucker in other places in pathname resolution
that check MAY_EXEC for directories; lose the _lite
from name, it's equivalent of full-blown inode_permission()
for its callers (albeit still lighter, since large parts
of generic_permission() do not apply for pure MAY_EXEC).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>