Merge flask framework and other stuff from master

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diff --git a/python/werkzeug/middleware/dispatcher.py b/python/werkzeug/middleware/dispatcher.py
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+"""
+Application Dispatcher
+======================
+
+This middleware creates a single WSGI application that dispatches to
+multiple other WSGI applications mounted at different URL paths.
+
+A common example is writing a Single Page Application, where you have a
+backend API and a frontend written in JavaScript that does the routing
+in the browser rather than requesting different pages from the server.
+The frontend is a single HTML and JS file that should be served for any
+path besides "/api".
+
+This example dispatches to an API app under "/api", an admin app
+under "/admin", and an app that serves frontend files for all other
+requests::
+
+    app = DispatcherMiddleware(serve_frontend, {
+        '/api': api_app,
+        '/admin': admin_app,
+    })
+
+In production, you might instead handle this at the HTTP server level,
+serving files or proxying to application servers based on location. The
+API and admin apps would each be deployed with a separate WSGI server,
+and the static files would be served directly by the HTTP server.
+
+.. autoclass:: DispatcherMiddleware
+
+:copyright: 2007 Pallets
+:license: BSD-3-Clause
+"""
+
+
+class DispatcherMiddleware(object):
+    """Combine multiple applications as a single WSGI application.
+    Requests are dispatched to an application based on the path it is
+    mounted under.
+
+    :param app: The WSGI application to dispatch to if the request
+        doesn't match a mounted path.
+    :param mounts: Maps path prefixes to applications for dispatching.
+    """
+
+    def __init__(self, app, mounts=None):
+        self.app = app
+        self.mounts = mounts or {}
+
+    def __call__(self, environ, start_response):
+        script = environ.get("PATH_INFO", "")
+        path_info = ""
+
+        while "/" in script:
+            if script in self.mounts:
+                app = self.mounts[script]
+                break
+
+            script, last_item = script.rsplit("/", 1)
+            path_info = "/%s%s" % (last_item, path_info)
+        else:
+            app = self.mounts.get(script, self.app)
+
+        original_script_name = environ.get("SCRIPT_NAME", "")
+        environ["SCRIPT_NAME"] = original_script_name + script
+        environ["PATH_INFO"] = path_info
+        return app(environ, start_response)