Remove Jan Wieck's name from copyrights, and put in standard

src/pl/plpgsql/src/gram.y

src/pl/plpgsql/src/pl_comp.c

src/pl/plpgsql/src/pl_exec.c

src/pl/plpgsql/src/pl_funcs.c

src/pl/plpgsql/src/pl_handler.c

src/pl/plpgsql/src/plpgsql.h

src/pl/plpgsql/src/scan.l