Add flag to stop always checking the form body for the override flag

Author: Adam Hathcock

src/Nancy/Request.cs

@@ -307,10 +307,13 @@ private void RewriteMethod()
             var overrides =
                 new List<Tuple<string, string>>
                 {
-                    Tuple.Create("_method form input element", (string)this.Form["_method"]),
-                    Tuple.Create("X-HTTP-Method-Override form input element", (string)this.Form["X-HTTP-Method-Override"]),
                     Tuple.Create("X-HTTP-Method-Override header", this.Headers["X-HTTP-Method-Override"].FirstOrDefault())
                 };
+            if (!StaticConfiguration.DisableXHttpMethodOverrideBodyDiscovery)
+            {
+                overrides.Add(Tuple.Create("_method form input element", (string)this.Form["_method"]));
+                overrides.Add(Tuple.Create("X-HTTP-Method-Override form input element", (string)this.Form["X-HTTP-Method-Override"]));
+            }
 
             var providedOverride =
                 overrides.Where(x => !string.IsNullOrEmpty(x.Item2))

src/Nancy/StaticConfiguration.cs

@@ -55,6 +55,14 @@ public static bool DisableErrorTraces
         [Description("Enables explicit HEAD routing and disables the usage of GET routes for HEAD requests.")]
         public static bool EnableHeadRouting { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether or not to disable the discovery of the X-HTTP-Method-Override flag in a request body.
+        /// This can be in the headers or posted form body of a request.  This flag will disable the discovery of this 
+        /// flag in the body of a request to avoid buffering the request body.
+        /// </summary>
+        [Description("Gets or sets a value indicating whether or not to disable the discovery of the X-HTTP-Method-Override flag in a request body.")]
+        public static bool DisableXHttpMethodOverrideBodyDiscovery { get; set; }
+
         /// <summary>
         /// Gets a value indicating whether we are running in debug mode or not.
         /// Checks the entry assembly to see whether it has been built in debug mode.