Do not cache objects used in the Add Package Reference dialog so changes to the registered package sources are seen in the dialog.

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

@@ -15,9 +15,7 @@ namespace ICSharpCode.PackageManagement
 		
 		public AddPackageReferenceViewModel AddPackageReferenceViewModel {
 			get {
-				if (addPackageReferenceViewModel == null) {
 				CreateAddPackageReferenceViewModel();
-				}
 				return addPackageReferenceViewModel;
 			}
 		}