A recent commit introduced resolving of S5B proxy domain names to their IPv4 and IPv6 addresses. With that a proxy identified by a JID can have more than one host and we try them in parallel until the first succeeds. The old code just handled one host per proxy JID and a failed IPv6 attempt would override the succeeded connection. The code uses shared pointers and the succeeded connecting is deallocated and disconnected when it is replaced with the failing IPv6 connection. The result is the proxy server complaining that we are not connected as we try to activate the proxy stream. This commit changes the the proxy management to handle multiple connections per proxy JID. Failing connections are removed from the proxy sessions data structure. With the first succeeding connections, others are stopped and also removed. Test-Information: Tested on Linux (Elementary OS 0.2) with "Swiften/QA/FileTransferTest/FileTransferTest 4 4", which forces the use of SOCKS5 bytestream proxy. Change-Id: If3071c3d058e1040556bb72702bf83f4f5f25334