norm_engine update with no encoder_base_t::has_data() dependency

I managed to refactor the norm_engine code so it doesn't need to use the deprecated has_data() method.  I managed, per Martin Hurton's suggestion, to use the zero return value of the encode() method as the needed end of message cue.  So this will build with "./configure --with-norm=<norm source tree path>".   The NRL norm-1.5b3 source code version is needed and the full src-norm-1.5b3.tgz tarball will appear on the NORM downloads site shortly.  I will update the "NORM notes"' Wiki page accordingly.