stage tests: ensure we can stage conflicts

A file should be ignored when it does not exist in the repository,
but conflicts should absolutely qualify as "existing in the
repository".  Ensure that we can stage ignored files correctly.

Author: ethomson

LibGit2Sharp.Tests/StageFixture.cs

@@ -350,5 +350,27 @@ public void IgnoredFilesAreOnlyStagedIfTheyreInTheRepo(string filename, FileStat
                 Assert.Equal(expected, repo.RetrieveStatus(filename));
             }
         }
+
+        [Theory]
+        [InlineData("ancestor-and-ours.txt", FileStatus.Unaltered)]
+        [InlineData("ancestor-and-theirs.txt", FileStatus.NewInIndex)]
+        [InlineData("ancestor-only.txt", FileStatus.Nonexistent)]
+        [InlineData("conflicts-one.txt", FileStatus.ModifiedInIndex)]
+        [InlineData("conflicts-two.txt", FileStatus.ModifiedInIndex)]
+        [InlineData("ours-only.txt", FileStatus.Unaltered)]
+        [InlineData("ours-and-theirs.txt", FileStatus.ModifiedInIndex)]
+        [InlineData("theirs-only.txt", FileStatus.NewInIndex)]
+        public void CanStageConflictedIgnoredFiles(string filename, FileStatus expected)
+        {
+            var path = SandboxMergedTestRepo();
+            using (var repo = new Repository(path))
+            {
+                File.WriteAllText(Path.Combine(repo.Info.WorkingDirectory, ".gitignore"),
+                    String.Format("{0}\n", filename));
+
+                repo.Stage(filename);
+                Assert.Equal(expected, repo.RetrieveStatus(filename));
+            }
+        }
     }
 }