* Dht: automatic listen multiplexing, resulting in reduction of network usage when performing multiple listen operations on the same key. * Dht, DhtRunner: new `listen()` API method with callback argument allowing to be informed of value expiration. The callback has the following signature: ```c++ bool(const std::vector<std::shared_ptr<dht::Value>& values, bool expired>) ``` * Dht: added value cache used by above features * network: added value expiration and refresh signals for listen operations * tests: added automated unit tests using CppUnit Since 1.7.0rc7: * proxy server: fix deadlock * proxy server: improve performance