Check if any control was changed inside a block of code.

When needing to check if GUI.changed is set to true inside a block of code, wrap the code inside BeginChangeCheck () and EndChangeCheck () like this:

	EditorGUI.BeginChangeCheck ();
	
	// Block of code with controls
	// that may set GUI.changed to true.
	
	if (EditorGUI.EndChangeCheck ()) {
		// Code to execute if GUI.changed
		// was set to true inside the block of code above.
	}

EndChangeCheck will only return true if GUI.changed was set to true inside the block, but GUI.changed will be true afterwards both if it was set to true inside and if it was already true to begin with.