maint: Use parentheses around condition for switch(),while(),if() statements. * libinterp/corefcn/dirfns.cc, libinterp/octave-value/ov-fcn-handle.cc, liboctave/array/Sparse.cc, scripts/image/rgb2ind.m, scripts/io/importdata.m, scripts/io/strread.m, scripts/optimization/fminbnd.m, scripts/optimization/sqp.m, scripts/plot/graphics_toolkit.m, scripts/plot/hdl2struct.m, scripts/plot/legend.m, scripts/plot/print.m, scripts/plot/printd.m, scripts/plot/private/__contour__.m, scripts/plot/private/__go_draw_axes__.m, scripts/plot/struct2hdl.m, scripts/polynomial/polyeig.m, scripts/sparse/bicg.m, scripts/specfun/ellipke.m, scripts/special-matrix/gallery.m, scripts/ui/errordlg.m, scripts/ui/helpdlg.m, scripts/ui/inputdlg.m, scripts/ui/listdlg.m, scripts/ui/questdlg.m, scripts/ui/warndlg.m: Use parentheses around condition for switch(),while(),if() statements.

--- a/scripts/plot/print.m
+++ b/scripts/plot/print.m
@@ -495,7 +495,7 @@
       if (opts.tight_flag)
         cmd = "--copy --bbox";
       elseif (! isempty (opts.preview))
-        switch opts.preview
+        switch (opts.preview)
         case "tiff"
           cmd = sprintf ("--add-%s-preview --device tiffg3", opts.preview);
         case {"tiff6u", "tiff6p", "metafile"}
@@ -617,7 +617,7 @@
     opts.name = opts.name(1:n-1);
   endif
   latexfile = strcat (opts.name, ".tex");
-  switch opts.devopt
+  switch (opts.devopt)
   case {"pdflatexstandalone"}
     packages = "\\usepackage{graphicx,color}";
     graphicsfile = strcat (opts.name, "-inc.pdf");