policycoreutils: sandbox: check for paths up front

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

This patch looks good to me. acked.

Need this so that we can ship sandbox command without X. -----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.11 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAk5Ws08ACgkQrlYvE4MpobPkegCeNlt2z/dSuRDDiOffwmUORHk0 IfcAoIQadmmT+x4fCNet2n5+28J+l1zT
=EWyr
-----END PGP SIGNATURE-----