Sometimes the default device node might not exist when reevaluating endpoints
for the first time on startup, so the policy would link endpoints to another
device node. Then, the default device node appears and the policy moves the
endpoints to the default device node while the previous link has not finish its
activation yet. This race condition can cause endpoint links to fail when being
activated. Delaying the reevaluation of endpoint links until the first client
link is created avoids this issue.
The policy scripts can handle now client nodes that want to be linked with other
client nodes. This is needed for nodes created by the Pulse Audio Volume Control
to monitor audio comming from other application client nodes.
Plugin() is confusing because it's not a constructor, it just finds
an existing instance of a plugin object. All other camel-case
functions are constructors in the current lua API.
