BaseType.h: Added a little text to the ptr_duplicate() documentaion.
BaseType.h: Added a little text to the ptr_duplicate() documentaion.

OPENDAP/libdap,OPENDAP/libdap4,OPENDAP/libdap,OPENDAP/libdap4,OPENDAP/libdap,OPENDAP/libdap4,OPENDAP/libdap,OPENDAP/libdap4,OPENDAP/libdap4,OPENDAP/libdap4