Allow NewInWorkdir files when checking out a PR

These might be build or tool artefacts that shouldn't prevent a PR from being checked out.

Author: jcansdale

src/GitHub.App/Services/PullRequestService.cs

@@ -89,7 +89,22 @@ public IObservable<string> GetPullRequestTemplate(ILocalRepositoryModel reposito
         public IObservable<bool> IsWorkingDirectoryClean(ILocalRepositoryModel repository)
         {
             var repo = gitService.GetRepository(repository.LocalPath);
-            return Observable.Return(!repo.RetrieveStatus().IsDirty);
+            var isClean = !IsFilthy(repo.RetrieveStatus());
+            return Observable.Return(isClean);
+        }
+
+        static bool IsFilthy(RepositoryStatus status)
+        {
+            if (status.IsDirty)
+            {
+                // This is similar to IsDirty, but also allows NewInWorkdir files
+                return status.Any(entry =>
+                    entry.State != FileStatus.Ignored &&
+                    entry.State != FileStatus.Unaltered &&
+                    entry.State != FileStatus.NewInWorkdir);
+            }
+
+            return false;
         }
 
         public IObservable<Unit> Pull(ILocalRepositoryModel repository)