GUI: support for octave arguments and integrate with run-octave. * src/octave.h (octave_initialize_interpreter, octave_execute_interpreter): New functions. (octave_cmdline_argc, octave_cmdline_argv, octave_embedded): New variables. * src/octave.cc (octave_cmdline_argc, octave_cmdline_argv, octave_embedded): New variables. (octave_initialize_interpreter, octave_execute_interpreter): New functions. (octave_main): Rewrite using them. * run-octave.in (octave_executable): New variable. (-gui): New option flag. * gui/src/octave-adapter/octave-main-thread.cc (octave_main_thread::run): Use octave_execute_interpreter. * gui/src/octave-gui.cc (dissociate_terminal): New function. (main): Use it. Also use octave_initialize_interpreter.