Added an option for netty connection pool to limit the time when connection can be put back to pool.
In case of Amazon Cloud DNS records can change in seconds, and taking into account that AHC caches already resolved connection and never re-resolve DNS records if response if ok, introducing option to limit life for cached connection, to be able to gracefully route traffic to new host in case dns records changed.

Conflicts:

	src/main/java/com/ning/http/client/AsyncHttpClientConfig.java
	src/main/java/com/ning/http/client/providers/netty/NettyConnectionsPool.java
Uses DateUtil.millisTime() instead of System.currentTimeMillis()
Merge pull request #310 from kumai/feature/connection-ttl

Added an option for netty connection pool to limit the time when connect...