Change return type of resource counts to unsigned.

src/cdi_int.c

src/cdi_int.h

src/grid.c

src/grid.h

src/institution.c

src/model.c

src/pio_interface.c

src/pio_server.c

src/resource_handle.c

src/resource_handle.h

src/stream.c

src/varscan.c

src/vlist.c

src/zaxis.c

src/zaxis.h