Add module with support for (patched) Trilead SSH2 (SVNKit fork)

https://github.com/ymnk/jsch-agent-proxy/pull/9
added a module to provide a factory to get an appropriate connector.

* introduced a module jsch-agent-proxy-connector-factory,
* introduced com.jcraft.agentproxy.ConnectorFatory,
* introduced the static method ConnectorFatory.getDefault() to get a connector.

https://github.com/ymnk/jsch-agent-proxy/pull/10
fixed a bug in checking the availability of usocket factories.
Merge remote-tracking branch 'upstream/issue9/support_for_trileadssh2'

Conflicts:
	examples/pom.xml
Fix compilation of SshjWithAgentProxy example (needs newer compiler -source flag)
Use new ConnectorFactory in library-specific examples