Grok "[no]brushspacing" commandline/config option

For forthcoming feature

src/parse.h

@@ -14,6 +14,7 @@ struct cfginfo
   const char *colorfile;
   const char *datadir;
   const char *disable_label;
+  const char *disable_brushspacing;
   const char *disable_magic_controls;
   const char *disable_shape_controls;
   const char *disable_print;