Actually, you owning the copyright makes you the rightsholder. You dictate the terms of use to anyone who uses the code. Those terms are spelled out in license.txt. Finally, license.txt says you reserve the right to revoke usage of the solidcoin codebase from anyone.
As for copyright and bitcoin, the bitcoin code is distributed with the following license:
"Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software."
Once I download the bitcoin code, I can do with it as I wish, as long as I include that notice at the top of the files.
Solidcoin code and all of its derivatives will always be under the control of Coinhunter (unless the license changes).