Decrypt lazily, on the first read(), otherwise the password
strengthening calculations only allow us to traverse 7z archives
using getNextEntry() at a rate of about 1 per second with
100% CPU usage.

Go back to extending InputStream after all, its semantics are necessary.



git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1483531 13f79535-47bb-0310-9956-ffa450edef68