has_color() performance fixes

Performance profiling showed that multiple strcmpi() calls were
occurring each and every time a character was going to the map.

This update:
- honors the WC_COLOR capability
- It allows a window-port to control individual color availability should the window-port wish to do so.
- Makes checking on the individual colors for the active window-port is a straightforward table lookup at the CLR_ offset.

iflags.use_color remains a master on/off switch for use of color, regardless of the capability
compiled into the game (default TRUE).

The has_color() routine, which is now a shared routine in src/windows.c, could likely be made
into a simple macro to eliminate the function call, but this update does not go that far.

This hits a lot of port files due to the window-port interface change, mostly cookie-cutter.

sys/winnt/nttty.c

@@ -790,6 +790,7 @@ init_ttycolor()
 }
 #endif /* TEXTCOLOR */
 
+#if 0
 int
 has_color(int color)
 {
@@ -803,6 +804,7 @@ has_color(int color)
     else
         return 0;
 }
+#endif
 
 int
 term_attr_fixup(int attrmask)

sys/winnt/stubs.c

@@ -114,12 +114,6 @@ backsp()
     return;
 }
 
-int
-has_color(int color)
-{
-    return 1;
-}
-
 #ifndef NO_MOUSE_ALLOWED
 void
 toggle_mouse_support()