doc: Periodic spellcheck of the documentation. * doc/interpreter/doccheck/aspell-octave.en.pws: Update Octave-specific Aspell dictionary. * doc/interpreter/contrib.txi, doc/interpreter/errors.txi, doc/interpreter/expr.txi, doc/interpreter/io.txi, doc/interpreter/preface.txi, doc/interpreter/sparse.txi, doc/interpreter/stmt.txi, doc/interpreter/strings.txi, libinterp/corefcn/qz.cc, libinterp/dldfcn/ccolamd.cc, libinterp/dldfcn/fftw.cc, libinterp/interpfcn/graphics.cc, scripts/general/structfun.m, scripts/image/ind2rgb.m, scripts/image/rgb2ind.m, scripts/io/importdata.m, scripts/linear-algebra/duplication_matrix.m, scripts/linear-algebra/housh.m, scripts/miscellaneous/mkoctfile.m, scripts/plot/comet3.m, scripts/plot/gco.m, scripts/plot/legend.m, scripts/plot/print.m, scripts/signal/fftshift.m, scripts/signal/periodogram.m, scripts/sparse/pcg.m, scripts/statistics/tests/f_test_regression.m, scripts/statistics/tests/t_test_regression.m, scripts/strings/strjoin.m, scripts/strings/strsplit.m: Correct spellings or add @nospell macro.

--- a/scripts/miscellaneous/mkoctfile.m
+++ b/scripts/miscellaneous/mkoctfile.m
@@ -53,13 +53,13 @@
 ## @item -R DIR
 ## Add the run-time path to the link command.
 ##
-## @item -Wl,@dots{}
-## Pass flags though the linker like "-Wl,-rpath=@dots{}".
+## @item @nospell{-Wl,@dots{}}
+## Pass flags though the linker like @nospell{"-Wl,-rpath=@dots{}"}.
 ## The quotes are needed since commas are interpreted as command
 ## separators.
 ##
 ## @item -W@dots{}
-## Pass flags though the compiler like "-Wa,OPTION".
+## Pass flags though the compiler like @nospell{"-Wa,OPTION"}.
 ##
 ## @item -c
 ## Compile but do not link.