[SSSD] [PATCH] Allow more libldap debugging

[Jakub Hrozek]

This patch should not be pushed to master, but I would like to get it
reviewed anyway.

It should be used to provide a custom build for users experiencing cases
where ldap_search_ext would block (c.f.
https://bugzilla.redhat.com/show_bug.cgi?id=728343)

For example:
export SSSD_DEBUG_LDAP_SEARCH="0xffff"
would set LDAP_DEBUG_ANY

The attached patch applies cleanly on the RHEL6.1 branch. I also have a
version that applies on master/1.5 if needed.