Cleanup and make better use of the stream API in the jrtfs code

Paul Sandoz suggested several improvements to the jrtfs implementation during the code review for the first push of JEP 220 to JDK 9. These should be examined and perhaps taken on board as this code evolves.

http://mail.openjdk.java.net/pipermail/jigsaw-dev/2014-December/004083.html