Rename pioNamespaceSetActive and make part of core interface.

examples/pio/collectData.c

examples/pio/collectData2003.F90

examples/pio/collectDataNStreams.c

examples/pio/compareResourcesArray.c

src/cdi.h

src/cdi.inc

src/cdiFortran.c

src/cdipio.h

src/cdipio.inc

src/cdipioFortran.c

src/namespace.c

src/namespace.h

src/pio_client.c

src/resource_handle.c

tests/pio_write.c

tests/test_resource_copy.c