Extended former conversion from DRA->DBA to handle
the case where some SCC is not DBA-realizable.

* src/dstarparse/dra2dba.cc: Rename as...
* src/dstarparse/dra2ba.cc: ... this.
(dra_to_dba, dra_to_dba_worker): Rename as...
(dra_to_ba, dra_to_ba_worker): ... these and extend.
* src/dstarparse/Makefile.am, src/dstarparse/public.hh,
src/dstarparse/dstar2tgba.cc, src/dstarparse/nra2nba.cc: Adjust.
* NEWS: Update the description of dstar2tgba accordingly.