doc: Miscellaneous small tweaks to documentation for consistency. * doc/interpreter/external.txi: Don't group EXAMPLEFILEs which are longer than 20 lines. * doc/interpreter/oop.txi: Don't group EXAMPLEFILEs which are longer than 20 lines. * doc/interpreter/octave.texi: Eliminate trailing whitespace. * doc/interpreter/tips.txi: Eliminate trailing whitespace. * examples/mysparse.c: Eliminate trailing whitespace. * scripts/miscellaneous/compare_versions.m: use @qcode macro. * scripts/plot/gnuplot_binary.in: use @qcode macro. * scripts/statistics/tests/kruskal_wallis_test.m: use @cite macro.