Eagerly dispose of Remotes

This is a continuation of #1249. Since Remotes are now disposable we
should eagerly clean up their resources rather than wait for GC to call
the destructor.

Author: niik

LibGit2Sharp/BranchUpdater.cs

@@ -154,7 +154,7 @@ private void SetUpstreamRemote(string remoteName)
                 if (!remoteName.Equals(".", StringComparison.Ordinal))
                 {
                     // Verify that remote exists.
-                    repo.Network.Remotes.RemoteForName(remoteName);
+                    using (repo.Network.Remotes.RemoteForName(remoteName)) { }
                 }
 
                 repo.Config.Set(configKey, remoteName);
@@ -183,8 +183,10 @@ private void GetUpstreamInformation(string canonicalName, out string remoteName,
             {
                 remoteName = Proxy.git_branch_remote_name(repo.Handle, canonicalName, true);
 
-                Remote remote = repo.Network.Remotes.RemoteForName(remoteName);
-                mergeBranchName = remote.FetchSpecTransformToSource(canonicalName);
+                using (Remote remote = repo.Network.Remotes.RemoteForName(remoteName))
+                {
+                    mergeBranchName = remote.FetchSpecTransformToSource(canonicalName);
+                }
             }
             else
             {

LibGit2Sharp/RepositoryExtensions.cs

@@ -221,8 +221,10 @@ public static void Fetch(this IRepository repository, string remoteName, FetchOp
             Ensure.ArgumentNotNull(repository, "repository");
             Ensure.ArgumentNotNullOrEmptyString(remoteName, "remoteName");
 
-            Remote remote = repository.Network.Remotes.RemoteForName(remoteName, true);
-            repository.Network.Fetch(remote, options);
+            using (Remote remote = repository.Network.Remotes.RemoteForName(remoteName, true))
+            {
+                repository.Network.Fetch(remote, options);
+            }
         }
 
         /// <summary>