added public swap method to replace a middleware

stack item

README.md

@@ -75,6 +75,7 @@ All this middleware does is check if there is a GET or a POST variable by the na
 * `Rack::add($name, $file = null)` — Add middleware class with name `$name`, and require file `$file` if set, and file exists.
 * `Rack::insert_before($target, $name, $file = null)` — Same as `Rack::add()`, except that instead of placing the new middleware at the end of the stack, it is inserted before the middleware `$name`.
 * `Rack::insert_after($target, $name, $file = null)` — Same as `Rack::insert_before()`, except new middleware is inserted after `$target`.
+* `Rack::swap($target, $name, $file = null)` — Replace `$target` middleware with `$name`.
 * `Rack::init($middleware = array())` — Can optionally be used as a simpler way to start Rack, as it takes an array of strings representing the stack classes. It also starts output buffering, so anything echoed within a stack class, will not be output till after Rack has output it's headers. Is also automatically called to start output buffering if needed the first time you call `Rack::add()`, `Rack::insert_before()`, or `Rack::insert_after()`.
 * `Rack::not_found()` — A shortcut method you can use when you want to return a 404 Not Found error status/page. It simply returns `array(404, array("Content-Type" => "text/html"), "Not Found")`.
 * `Rack::run()` — Initiate and execute the Rack stack.

lib/rack.php

@@ -105,6 +105,28 @@ class Rack {
 	}
 	
 	
+	public static function swap ($target, $name, $file = null) {
+		if ( !self::$constructed ) {
+			if ( array_key_exists($target, self::$middleware) ) {
+				$keys = array_keys(self::$middleware);
+				$length = count($keys);
+				$middleware = array();
+				for ( $i=0; $i < $length; $i++ ) {
+					if ( $keys[$i] == $target ) {
+						$middleware[$name] = true;
+					} else {
+						$middleware[$keys[$i]] =& self::$middleware[$keys[$i]];
+					}
+				}
+				self::$middleware = $middleware;
+				self::require_file($file);
+				return false;
+			}
+		}
+		return false;
+	}
+	
+	
 	public static function not_found () {
 		return array(404, array("Content-Type" => "text/html"), "Not Found");
 	}