Add BIST tests for various quasi-internal m-files. * __actual_axis_position__.m, __default_plot_options__.m, __next_line_color__.m, __next_line_style__.m, __pltopt__.m, __have_feature__.m, __printf_assert__.m, __prog_output_assert__.m, __run_test_suite__.m: Add BIST tests for various quasi-internal m-files.

--- a/scripts/testfun/__have_feature__.m
+++ b/scripts/testfun/__have_feature__.m
@@ -33,3 +33,7 @@
   endif
 endfunction
 
+
+## No test coverage for internal function.  It is tested through calling fcn.
+%!assert (1)
+