load svctype .so earlier in the process...

We can go ahead and load the actual plugin while doing the
first phase of service_types processing, so long as we don't actually
call its add_svctype/add_monitor calls yet.  This allows for
some earlier failure detection, but more importantly it allows
us to distinguish (by presence/absence of certain callbacks)
multiple types of monitoring plugins while add_monitor() is
being called by resolver plugin configs.
core support for CNAME monitoring
mon-plugin support for CNAME monitoring
Add CNAME monitoring to plugin_weighted