Heretic and Hexen goes GNU GPLv2

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The source code for Heretic and Hexen has been re-released under the GNU General Public License, and is now available from Sourceforge. This release will allow GPL Doom source ports to freely integrate support for Heretic and Hexen without requiring the code to be rewritten from scratch or to be emulated through empirical testing. The door is also now open for new ports such as "Chocolate" Heretic and Hexen, and for such ports to be distributed in free software packages.

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