Short-circuit checkintool if the checkin dialog isn't available.

GitTfs.Vs2008/TfsHelper.Vs2008.cs

@@ -14,6 +14,8 @@ namespace Sep.Git.Tfs.VsCommon
             get { return typeof(TeamFoundationServer).Assembly.GetName().Version.ToString() + " (MS)"; }
         }
 
+        public bool CanShowCheckinDialog { get { return false; } }
+
         public bool ShowCheckinDialog(IWorkspace workspace, IPendingChange[] pendingChanges, IEnumerable<IWorkItemCheckedInfo> checkedInfos, string checkinComment)
         {
             throw new NotImplementedException();

GitTfs.Vs2010/TfsHelper.Vs2010.cs

@@ -41,6 +41,8 @@ namespace Sep.Git.Tfs.VsCommon
             }
         }
 
+        public bool CanShowCheckinDialog { get { return true; } }
+
         public bool ShowCheckinDialog(IWorkspace workspace, IPendingChange[] pendingChanges, 
             IEnumerable<IWorkItemCheckedInfo> checkedInfos, string checkinComment)
         {

GitTfs/Commands/CheckinTool.cs

@@ -35,7 +35,12 @@ namespace Sep.Git.Tfs.Commands
         {
             return _writer.Write(refToCheckin, changeset =>
             {
-                changeset.Remote.CheckinTool(refToCheckin, changeset);
+                if (changeset.Remote.Tfs.CanShowCheckinDialog)
+                    changeset.Remote.CheckinTool(refToCheckin, changeset);
+                else
+                    throw new Exception(
+                        "checkintool does not work with this TFS version (" + changeset.Remote.Tfs.TfsClientLibraryVersion + ").",
+                        new[] {"Try installing the VS2010 edition of Team Explorer."});
                 return GitTfsExitCodes.OK;
             });
         }

GitTfs/Core/TfsInterop/ITfsHelper.cs

@@ -18,6 +18,7 @@ namespace Sep.Git.Tfs.Core.TfsInterop
         IChangeset GetChangeset(int changesetId);
         bool MatchesUrl(string tfsUrl);
         bool HasShelveset(string shelvesetName);
+        bool CanShowCheckinDialog { get; }
         bool ShowCheckinDialog(IWorkspace workspace, IPendingChange[] pendingChanges, IEnumerable<IWorkItemCheckedInfo> checkedInfos, string checkinComment);
     }
 }