ngcgui,pyngcgui: add nom2 option

By default, [py]ngcgui terminates created ngc files with M2.

M2 (Program End) has a number of defined side effects that
may not be wanted.  This patch provides an option (nom2) such
that the created ngc file is started and ended with a single
percent (%) character and no terminating M2.

Option format:
  command_line: -N | --nom2
Inifile:
  NGCGUI_OPTS = ... nom2 ...

(Note: [py]ngcgui has always ignored M2 lines that follow an
endsub in the subroutines it processes)

thanks to Rick (rng3) for the suggestion