add "NODE_" prefix to NodeType enum

util.h

@@ -11,11 +11,11 @@
 #define WM_HORIZ_BOT  1
 
 typedef enum NodeType {
-    VERTICAL,
-    HORIZONTAL,
-    TAB,
-    CLIENT,
-    COUNT
+    NODE_VERTICAL,
+    NODE_HORIZONTAL,
+    NODE_TAB,
+    NODE_CLIENT,
+    NODE_COUNT
 } NodeType;
 
 typedef struct TreeNode TreeNode;