The server test used the wrong name.
MySQL users test loaded multiple modules in one function call and wasn't
appropriate for an internal test suite test as it requires a working
installation.
The cache filter didn't set the library paths before trying to load
modules.
The binlogrouter was missing a NULL check which caused a crash.
The dbusers.c was a MySQL protocol specific file which was used directly
by some of the modules.
Added a new return value for the loadusers authenticator entry point which
allows fatal failures to occur when users are loaded. Currently this is
only taken into notice when the service is first started. If a listener
later returns a fatal error, it is only logged but the service stays in
operation.
Moved the MySQLAuth authenticator sources and the tests that relate to
this module into a subdirectory in the authenticator
directory. Eventually, all authenticators could have a subdirectory of
their own.
