Support slashes in release tags (#12864)

Fix #12861

Signed-off-by: Andrew Thornton <art27@cantab.net>

routers/repo/release.go

 	writeAccess := ctx.Repo.CanWrite(models.UnitTypeReleases)
 	ctx.Data["CanCreateRelease"] = writeAccess && !ctx.Repo.Repository.IsArchived
 
-	release, err := models.GetRelease(ctx.Repo.Repository.ID, ctx.Params("tag"))
+	release, err := models.GetRelease(ctx.Repo.Repository.ID, ctx.Params("*"))
 	if err != nil {
 		if models.IsErrReleaseNotExist(err) {
 			ctx.NotFound("GetRelease", err)

routers/routes/routes.go

 	m.Group("/:username/:reponame", func() {
 		m.Group("/releases", func() {
 			m.Get("/", repo.Releases)
-			m.Get("/tag/:tag", repo.SingleRelease)
+			m.Get("/tag/*", repo.SingleRelease)
 			m.Get("/latest", repo.LatestRelease)
-		}, repo.MustBeNotEmpty, context.RepoRef())
+		}, repo.MustBeNotEmpty, context.RepoRefByType(context.RepoRefTag))
 		m.Group("/releases", func() {
 			m.Get("/new", repo.NewRelease)
 			m.Post("/new", bindIgnErr(auth.NewReleaseForm{}), repo.NewReleasePost)