Made a checkMaxBrushRadius method for centralized use.

src/main/java/com/sk89q/worldedit/MaxBrushRadiusException.java

@@ -0,0 +1,10 @@
+package com.sk89q.worldedit;
+
+/**
+ * 
+ * Thrown when a maximum radius for a brush is reached.
+ *
+ */
+public class MaxBrushRadiusException extends MaxRadiusException {
+
+}