[VFS-484][SFTP] Update Jsch to 0.1.50 from 0.1.49.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/vfs/trunk@1511566 13f79535-47bb-0310-9956-ffa450edef68
[VFS-482] Wrong assertion messages in RAM provider test case. Fix change description in changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/vfs/trunk@1511567 13f79535-47bb-0310-9956-ffa450edef68