Add fieldnames.m which extensds fieldnames() to work on Java objects. Deprecate javafields. Rename old C++ fieldnames to __fieldnames__. * scripts/deprecated/javafields.m: Moved from scripts/java. Added deprecated warning. * scripts/java/javafields.m: Moved to scripts/deprecated. * scripts/general/fieldnames.m: New m-file which accepts Java, structure, or Octave objects as inputs. * libinterp/octave-value/ov-struct.cc(Ffieldnames): Renamed fieldnames to __fieldnames__ to avoid class with fieldnames.m. * scripts/deprecated/module.mk: Added javafields to deprecated build. * scripts/general/module.mk: Added fieldnames.m to build. * scripts/java/module.mk: Removed javafields.m from build.