Fixed checkstyle errors and javadoc warnings in Disruptor.java

To fix the first issue in issue #101 and also to address the javadoc warnings that java 8 spews out when building the disruptor, I updated the Disruptor.java file (there are still lots of other files with javadoc warnings).  No functionality was changed.  Builds and all tests pass under both java 7 and java 8 (tested on Linux only).