ADS support.

[Jeremy Allison]

Andrew,

	The ldap headers are broken on RedHat 6.2 (Samba HEAD
doesn't compile). We need to extend the autoconf tests so
that simply having ldap.h and krb5.h doesn't turn on ADS support,
we need to try and compile some sample code to see if it will
compile befoire turning on WITH_ADS.

This could cause the compile to break on many systems that have
these headers but have never tested with them (or have an older
ldapv2 version).

I'll get to it sometime in HEAD.....

Jeremy.