Add some more test coverage demonstrating the handling of .gitgnore file

Author: nulltoken

LibGit2Sharp.Tests/StatusFixture.cs

@@ -146,6 +146,8 @@ public void RetrievingTheStatusOfTheRepositoryHonorsTheGitIgnoreDirectives()
 
                 RepositoryStatus newStatus = repo.Index.RetrieveStatus();
                 newStatus.Untracked.Single().ShouldEqual(".gitignore");
+
+                repo.Index.RetrieveStatus(relativePath).ShouldEqual(FileStatus.Ignored);
             }
         }
     }

LibGit2Sharp/FileStatus.cs

@@ -45,7 +45,9 @@ public enum FileStatus
         /// </summary>
         Missing = (1 << 5), /* GIT_STATUS_WT_DELETED */
 
-        //TODO: Ignored files not handled yet
-        GIT_STATUS_IGNORED = (1 << 6), /* GIT_STATUS_IGNORED */
+        /// <summary>
+        ///   The file is <see cref="Untracked"/> but its name and/or path macthes an exclude pattern in a <c>gitignore</c> file.
+        /// </summary>
+        Ignored = (1 << 6), /* GIT_STATUS_IGNORED */
     }
 }