Adding more fallbacks for BufferingHelper temporary folder location

src/Microsoft.AspNet.Http.Core/BufferingHelper.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.IO;
-using Microsoft.AspNet.Http;
 using Microsoft.AspNet.WebUtilities;
 
 namespace Microsoft.AspNet.Http.Core
@@ -16,11 +15,12 @@ public static string TempDirectory
         {
             get
             {
-                var temp = Environment.GetEnvironmentVariable("ASPNET_TEMP");
-                if (string.IsNullOrEmpty(temp))
-                {
-                    temp = Environment.GetEnvironmentVariable("TEMP");
-                }
+                // Look for folders in the following order.
+                var temp = Environment.GetEnvironmentVariable("ASPNET_TEMP") ??     //  ASPNET_TEMP - User set temporary location.
+                           Environment.GetEnvironmentVariable("TEMP") ??            // TEMP - Points to AppData\Local on Windows.
+                           Environment.GetEnvironmentVariable("TMPDIR") ??          // TMPDIR - Temporary folder on Mac and some linux distributions.
+                           Environment.GetEnvironmentVariable("TMP") ??             // TMP
+                           "/tmp";                                                  // Fallback
 
                 if (!Directory.Exists(temp))
                 {

test/Microsoft.AspNet.Http.Core.Tests/BufferingHelperTests.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.IO;
+using Xunit;
+
+namespace Microsoft.AspNet.Http.Core.Tests
+{
+    public class BufferingHelperTests
+    {
+        [Fact]
+        public void GetTempDirectory_Returns_Valid_Location()
+        {
+            var tempDirectory = BufferingHelper.TempDirectory;
+            Assert.NotNull(tempDirectory);
+            Assert.True(Directory.Exists(tempDirectory));
+        }
+    }
+}