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.

%!function out = bug54490 ()
%!  global k;
%!  k = 1;
%!  out = 3;
%!endfunction

%!test <*54490>
%! global k;
%! k = 2;
%! a = [5, 6];
%! a(k) = bug54490 ();
%! assert (a, [5, 3]);
%! k = 2;
%! a = [5, 6];
%! [a(k)] = bug54490 ();
%! assert (a, [5, 3]);
%! clear -global k;  # cleanup after test