Allow saving external tool options when tools in the .NET SDK cannot be found.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/branches/3.0@3971 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ExternalToolPanel.cs

@@ -7,6 +7,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Text.RegularExpressions;
 using System.Windows.Forms;
 
 using ICSharpCode.Core;
@@ -151,9 +152,11 @@ namespace ICSharpCode.SharpDevelop.Gui.OptionPanels
 			List<ExternalTool> newlist = new List<ExternalTool>();
 			foreach (ExternalTool tool in ((ListBox)ControlDictionary["toolListBox"]).Items) {
 				if (!FileUtility.IsValidPath(StringParser.Parse(tool.Command))) {
+					if (!Regex.IsMatch(tool.Command, @"^\$\{SdkToolPath:[\w\d]+\.exe\}$")) {
 						MessageService.ShowError(String.Format("The command of tool \"{0}\" is invalid.", tool.MenuCommand));
 						return false;
 					}
+				}
 				if ((tool.InitialDirectory != String.Empty) && (!FileUtility.IsValidPath(tool.InitialDirectory))) {
 					MessageService.ShowError(String.Format("The working directory of tool \"{0}\" is invalid.", tool.MenuCommand));
 					return false;