Fixes: sites cannot run the new installer if they have /install directory

src/Umbraco.Web.UI/config/ClientDependency.config

@@ -10,7 +10,7 @@ NOTES:
 * Compression/Combination/Minification is not enabled unless debug="false" is specified on the 'compiliation' element in the web.config
 * A new version will invalidate both client and server cache and create new persisted files
 --> 
-<clientDependency version="394389720" fileDependencyExtensions=".js,.css" loggerType="Umbraco.Web.UI.CdfLogger, umbraco">
+<clientDependency version="1469612626" fileDependencyExtensions=".js,.css" loggerType="Umbraco.Web.UI.CdfLogger, umbraco">
 
   <!-- 
     This section is used for Web Forms only, the enableCompositeFiles="true" is optional and by default is set to true.

src/Umbraco.Web/Install/InstallHelper.cs

@@ -2,13 +2,14 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Configuration;
+using System.IO;
 using System.Linq;
 using System.Web;
 using System.Web.Script.Serialization;
 using System.Web.UI;
-
 using Umbraco.Core;
 using Umbraco.Core.Configuration;
+using Umbraco.Core.IO;
 using Umbraco.Core.Persistence;
 using Umbraco.Web.Install.InstallSteps;
 using Umbraco.Web.Install.Models;
@@ -65,6 +66,12 @@ namespace Umbraco.Web.Install
             return _installationType ?? (_installationType = IsBrandNewInstall ? InstallationType.NewInstall : InstallationType.Upgrade).Value;
         }
 
+        internal void DeleteLegacyInstaller()
+        {
+            if(Directory.Exists( IOHelper.MapPath( SystemDirectories.Install )))
+                Directory.Move(IOHelper.MapPath(SystemDirectories.Install), IOHelper.MapPath("~/app_data/temp/install_backup"));
+        }
+
         /// <summary>
         /// Checks if this is a brand new install meaning that there is no configured version and there is no configured database connection
         /// </summary>

src/Umbraco.Web/WebBootManager.cs

@@ -103,6 +103,9 @@ namespace Umbraco.Web
             renderer.Initialize("Umbraco.DependencyPathRenderer", new NameValueCollection { { "compositeFileHandlerPath", "~/DependencyHandler.axd" } });
             ClientDependencySettings.Instance.MvcRendererCollection.Add(renderer);
 
+            InstallHelper insHelper = new InstallHelper(UmbracoContext.Current);
+            insHelper.DeleteLegacyInstaller();
+
             return this;
         }