Clear dialog error messages when updating all NuGet packages.

src/AddIns/Misc/PackageManagement/Project/Src/PackagesViewModel.cs

@@ -375,6 +375,7 @@ namespace ICSharpCode.PackageManagement
 		void UpdateAllPackages()
 		{
 			try {
+				packageViewModelFactory.PackageManagementEvents.OnPackageOperationsStarting();
 				TryUpdatingAllPackages();
 			} catch (Exception ex) {
 				ReportError(ex);

src/AddIns/Misc/PackageManagement/Test/Src/UpdatedPackagesViewModelTests.cs

@@ -649,5 +649,16 @@ namespace PackageManagement.Tests
 			UpdateSolutionPackagesAction action = GetUpdateSolutionPackagesActionRun();
 			Assert.AreEqual(expectedLogger, action.Logger);
 		}
+		
+		[Test]
+		public void UpdateAllPackagesCommand_TwoPackagesBeingUpdated_PreviouslyLoggedMessagesAreCleared()
+		{
+			CreateViewModel();
+			ViewModelHasTwoPackagesThatCanBeUpdatedAfterReadingPackages();
+			
+			RunUpdateAllPackagesCommand();
+			
+			Assert.IsTrue(packageViewModelFactory.FakePackageManagementEvents.IsOnPackageOperationsStartingCalled);
+		}
 	}
 }