interface groundwork for core-side color decisions

(user-side decisions really, but as it stands right now
user-side decisions/options are made and processed by the core)

add a parameter to add_menu so color can be passed

win/win32/mhmsg.h

@@ -51,6 +51,7 @@ typedef struct mswin_nhmsg_add_menu {
     char accelerator;
     char group_accel;
     int attr;
+    int clr;
     const char *str;
     boolean presel;
     unsigned int itemflags;