Change mechanism to declare copyright, moving from source code into separate file included with distributions

The copyright information in our source needs to be cleaned up and corrected. In particular, we can place the copyright into a separate COPYRIGHT.txt file included in each distribution, and change the headers to refer to this file. Then the source only contains the license information (plus references to the copyright and authors files in the distribution). This is actually a much better way to handle copyrights (since the year and the copyright text is in one place, and can be annotated as required), yet does not change any rights on existing code.

Also, SVN is the master record for each individual contribution, so pending decision by the community, the "@author" tags would be removed from the code, which would refer to a new AUTHORS.txt file.

The content of the AUTHORS.txt, COPYRIGHT.txt, and new header are attached. Note that the Eclipse preferences need to be changed accordingly.