The GSS mechglue uses singly linked lists for mechanisms and mechanism objects,
to which new entries are inserted at the head. This breaks ordering of
mechanisms specified in OID sets and in /etc/gss/mech, as they will be back to
front. Use a tail queue instead so that new entries are inserted at the end.
Be consistent with other GSSAPI global variables. GSS_C_ATTR_LOCAL_LOGIN_USER
becomes a macro in gssapi.h that refers to an exported variable
__gss_c_attr_local_login_user
Change-Id: I2661d74cd0f760780f75b35f92d6b4f9112080dc
