Fix add-in unpacking issue

If an adding package is created on windows, the zip file entries
may contain backslashes. When unpacking on pack, the backslashes
need to be converted to regular slashes.

Mono.Addins.Setup/Mono.Addins.Setup/AddinPackage.cs

@@ -136,7 +136,12 @@ internal override void PrepareInstall (IProgressMonitor monitor, AddinStore serv
 			using (FileStream fs = new FileStream (packFile, FileMode.Open, FileAccess.Read)) {
 				ZipFile zip = new ZipFile (fs);
 				foreach (ZipEntry entry in zip) {
-					string path = Path.Combine (tempFolder, entry.Name);
+					string name;
+					if (Path.PathSeparator == '\\')
+						name = entry.Name.Replace ('/', '\\');
+					else
+						name = entry.Name.Replace ('\\', '/');
+					string path = Path.Combine (tempFolder, name);
 					string dir = Path.GetDirectoryName (path);
 					if (!Directory.Exists (dir))
 						Directory.CreateDirectory (dir);