Better ivar and param name (charsetName instead of charset).

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1534222 13f79535-47bb-0310-9956-ffa450edef68
Fix Javadoc nit.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1534223 13f79535-47bb-0310-9956-ffa450edef68