Update to autoconf 1.3 with aclocal from automake 1.4

 don't leak slap_op when op not in list
 don't leak abandon mutex
 use ch_malloc and friends

Plus have --enable-dns imply --enable-referrals unless --disable-referrals.

	use ldap_pvt_ routines (replacing old lthread impl)

Update configure based upon openldap.m4