maint: cleanup code in BIST tests to use Octave coding conventions. * data.cc: Use keyword "endfor" rather than bare "end". * file-io.cc, graphics.cc: Remove semicolon ';' at end of "end_try_catch" keyword. * variables.cc, bug-35448.tst, bug-53027.tst, bug-53579.tst, bug-53599.tst, bug-53956.tst, bug-55758.tst, global.tst: Use semicolon ';' after "global" variable declaration. * for.tst, io.tst: Delete semicolon ';' at end of "for" loop declaration. * struct.tst: Delete semicolon ';' at end of "function" declaration.

%!test <*55758>
%! global class_bug_55758_dtor_called;
%! class_bug_55758_dtor_called = false;
%!
%! assert (class_bug_55758 (5).value, 5);
%! assert (class_bug_55758_dtor_called);
%!
%! assert (class_bug_55758 (5)(1), 5);
%! assert (class_bug_55758_dtor_called);
%!
%! assert (size (class_bug_55758 (5)), [1, 1]);
%! assert (class_bug_55758_dtor_called);
%!
%! assert (numel (class_bug_55758 (5)), 1);
%! assert (class_bug_55758_dtor_called);
%! clear -global class_bug_55758_dtor_called;  # cleanup after test