Log daemonising failures

This also clears errno in the main function to ensure that no incorrect
errno value is logged on errors.
Small documentation improvements

This includes a number of minor changes to the documentation. This also
documents the children search scope (related to 2caeef4).
Use FreeBSD lib directory and SONAME on Dragonfly
Also extract policy controls on BIND failure

This ensures that controls returned by an LDAP server as part of a
failed BIND operation are also returned. This makes it possible to
distinguish between a wrong password and an expired password.

This also only logs the BIND operation result on DEBUG level (the error
is logged later on).
Improve error logging of user login failures