Make ktc_curpag generally available

Make ktc_curpag generally available

ktc_curpag isn't specific to a Kerberos v4 environment, so move it outside
the AFS_KERBEROS_ENV #ifdef.  Add it to the auth.h header and to the
exports from the shared libafsauthent.

Reviewed-on: http://gerrit.openafs.org/64
Verified-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>