Merge pull request #1173 from Pilchie/Fix1083

When validating references, ignore duplicates

src/VisualStudio/Core/Def/Implementation/ProjectSystem/AbstractProject.cs

@@ -1275,7 +1275,8 @@ private void ValidateReferences()
                 }
             }
 
-            var delta = vsproject.References.Count - noReferenceOutputAssemblies.Count - (_projectReferences.Count + _metadataReferences.Count);
+            var set = new HashSet<string>(vsproject.References.OfType<Reference>().Select(r => PathUtilities.IsAbsolute(r.Name) ? Path.GetFileNameWithoutExtension(r.Name) : r.Name), StringComparer.OrdinalIgnoreCase);
+            var delta = set.Count - noReferenceOutputAssemblies.Count - (_projectReferences.Count + _metadataReferences.Count);
             if (delta == 0)
             {
                 return;
@@ -1288,8 +1289,6 @@ private void ValidateReferences()
                 return;
             }
 
-            var set = new HashSet<string>(vsproject.References.OfType<Reference>().Select(r => PathUtilities.IsAbsolute(r.Name) ? Path.GetFileNameWithoutExtension(r.Name) : r.Name), StringComparer.OrdinalIgnoreCase);
-
             set.ExceptWith(noReferenceOutputAssemblies);
             set.ExceptWith(_projectReferences.Select(r => ProjectTracker.GetProject(r.ProjectId).DisplayName));
             set.ExceptWith(_metadataReferences.Select(m => Path.GetFileNameWithoutExtension(m.FilePath)));