Module signature checker and key manager

Module signature checker and key manager

Port to 2.6.39 following commit:

commit b0df24aa16fdaf7ccb0fb072a0f48b3f9b0c6b59
Author: David Howells <dhowells@redhat.com>
Date:   Wed Nov 11 15:47:32 2009 -0500

    Module signature checker and key manager

    Add a facility to retain public keys and to verify signatures made with those
    public keys, given a signature and crypto_hash of the data that was signed.

    Signed-Off-By: David Howells <dhowells@redhat.com>
    Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>
    Signed-off-by: Chris Mason <chris.mason@oracle.com>