Give mongoldap a 'debug' mode

The mongoldap tool is intended to produce useful, clear, reports for administrators setting up or debugging LDAP AuthZN deployments. However, if an issue arises in the actual implementation of the LDAP integration, noisy, unclear, diagnostic information would be useful. It should be possible to invoke mongoldap with '--debug' to print all the low priority informational messages printed by the LDAP subsystem.