Hide and disable color cursors option on Mac OS X (bug #18112)

It is known to cause severe lags that may render the cursor completely
unusable at times. This probably won't be solved until Wesnoth can run
on SDL 2.0.

changelog

@@ -33,6 +33,8 @@ Version 1.11.7+dev:
      all human player slots have been taken.
    * Change layout for advertized games in the MP lobby and add map icon.
    * Moved color cursors option to Advanced Preferences.
+   * Always hide and disable color cursors option on Mac OS X since it's known
+     to cause severe lags that render the cursor unusable.
  * WML engine:
    * WML variable turn_number is set correctly (to 1) in prestart and start
      events.  Previously, it retained its last value from the previous scenario

data/advanced_preferences.cfg

@@ -174,6 +174,7 @@
     default=no
 [/advanced_preference]
 
+#ifndef APPLE
 [advanced_preference]
     field=color_cursors
     name= _ "Show color cursors"
@@ -181,6 +182,7 @@
     type=boolean
     default=no
 [/advanced_preference]
+#endif
 
 #ifdef __UNUSED__
 [advanced_preference]

src/cursor.cpp

@@ -28,7 +28,13 @@
 
 static bool use_color_cursors()
 {
+#ifdef __APPLE__
+	// Color cursors on OS X are known to be unusable, so don't use them ever.
+	// See bug #18112.
+	return false;
+#else
 	return game_config::editor == false && preferences::use_color_cursors();
+#endif
 }
 
 static SDL_Cursor* create_cursor(surface surf)