AppArmor: file enforcement routines

AppArmor does files enforcement via pathname matching.  Matching is done
at file open using a dfa match engine.  Permission is against the final
file object not parent directories, ie. the traversal of directories
as part of the file match is implicitly allowed.  In the case of nonexistant
files (creation) permissions are checked against the target file not the
directory.  eg. In case of creating the file /dir/new, permissions are
checked against the match /dir/new not against /dir/.

The permissions for matches are currently stored in the dfa accept table,
but this will change to allow for dfa reuse and also to allow for sharing
of wider accept states.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>