Add the ability for users to prefix LDAP servers with "srv:" and "srv_raw:" so that the code automatically does the DNS lookups for SRV records.

Enhance mongoldap to advise users when they make mistakes around srv vs srv_raw.

When a user specifies "srv:<DNS NAME>", mongoldap will check and verify "_ldap._tcp.<DNS NAME>" exists for SRV. If an SRV record cannot be found, it will check "<DNS NAME>" for SRV, and warn the user they should use "srv_raw:<DNS_NAME>" instead. MongoLDAP will do the reverse check for "srv_raw:<DNS_NAME>" by checking for "_ldap._tcp.<DNS NAME>". When a user specifies "multi:<DNS_NAME>", mongoldap will check for "SRV" and suggest the user should use "srv_raw:<DNS_NAME>" instead.