connection pool: idle connection never closed

[weissi]

Currently, the pool keeps idle connections open indefinitely (or until the server closes). That is okay from a correctness point of view but may lead to a very large number of open connections when for example implementing a crawler.

[PopFlamingo]

@weissi Should this be a new global setting on the client that would apply to all of its connections?
Maybe we could set it to an acceptable default value, and if needed expose it as a new Configuration property the user can set.