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 <*53956>
%! global dtor2_called dtor4_called;
%!
%! dtor2_called = dtor4_called = 0;
%! x = bug53956_class_3 ();
%! clear x
%! assert (dtor2_called, 1);
%!
%! dtor2_called = dtor4_called = 0;
%! x = bug53956_class_4 ();
%! clear x
%! assert (dtor2_called, 1);
%! assert (dtor4_called, 1);
%!
%! clear -global dtor2_called dtor4_called;  # cleanup after test