Nice to have text advising customers that they need saslauthd if about to enable LDAP (was: Package manager should have a rule check for saslauthd similar to ssl )

In Sherlock, LDAP will be a new feature that will be supported on Enterprise builds on all platforms except Windows and MacOSX.

We need a check in the installer to make sure that we raise a error when this dependency is not installed. Very similar to the SSL check we already have.