fix license notices in source files and license files under GPLv2+
Previously a lot of files were referenced to GNU Public License 2.1,
which never existed.
All copyright attributions are kept the same.
int CheckRetainBuffer(void){ return 1;}void ValidateRetainBuffer(void){}void InValidateRetainBuffer(void){}void Retain(unsigned int offset, unsigned int count, void *p){}void Remind(unsigned int offset, unsigned int count, void *p){}