Relicense Subversion under the Apache License, Version 2.0.
* NOTICE: New.
* LICENSE: New.
* COPYING, subversion/LICENSE: Remove.
* subversion/libsvn_subr/opt.c (svn_opt__print_version_info): Note that the product as a whole is copyrighted by the SVN Corp, and that it contains contributions from many people, as referenced in NOTICE.
* subversion/bindings/swig/python/LICENSE_FOR_PYTHON_BINDINGS: Relicense the SVN parts under Apache 2.0.
* everywhere: Change copyright notices in file headers to reflect the Apache 2.0 license.