Cleanup: make symbolic names for CONF_bold_style bits.

CONF_bold_style is a pair of bit flags rather than an enum, so its
values aren't just BOLD_STYLE_FONT and BOLD_STYLE_COLOUR but also the
bitwise OR of them. (Hopefully not neither.)

config.c

@@ -2420,9 +2420,9 @@ void setup_config_box(struct controlbox *b, bool midsession,
     ctrl_radiobuttons(s, "Indicate bolded text by changing:", 'b', 3,
                       HELPCTX(colours_bold),
                       conf_radiobutton_handler, I(CONF_bold_style),
-                      "The font", I(1),
-                      "The colour", I(2),
-                      "Both", I(3));
+                      "The font", I(BOLD_STYLE_FONT),
+                      "The colour", I(BOLD_STYLE_COLOUR),
+                      "Both", I(BOLD_STYLE_FONT | BOLD_STYLE_COLOUR));
 
     str = dupprintf("Adjust the precise colours %s displays", appname);
     s = ctrl_getset(b, "Window/Colours", "adjust", str);