common_quakedef.h (and thus all files)
This solves a build break when the OpenGL includes are not in /usr/include,
since the OpenGL include path is only used when compiling files that use
OpenGL.
added "Portions" statement to the copyright statement
Please note, if you want to put a copyright notice on a source file stating that a portion of it is copyright yourself or another author please put "Portions Copyright...", if adding a seperate .c file that contains otherwise author(s) this doesn't apply.
