Allow Gogs to run from a suburl behind a reverse proxy. e.g. http://mydomain.com/gogs/

Conflicts:
	modules/setting/setting.go

Conflicts:
	templates/repo/release/list.tmpl
	templates/user/dashboard/dashboard.tmpl

Conflicts:
	routers/repo/setting.go

modules/middleware/context.go

@@ -187,7 +187,7 @@ func Contexter() macaron.Handler {
 			Session: sess,
 		}
 		// Compute current URL for real-time change language.
-		link := ctx.Req.RequestURI
+		link := setting.AppRootSubUrl + ctx.Req.RequestURI
 		i := strings.Index(link, "?")
 		if i > -1 {
 			link = link[:i]