register_module fails when url_prefix not previously set

[flowblok]

The following example (taken from the documentation, simplified) fails to work correctly.
The index() function is registered at / instead of /admin.

myapp/init.py:
from flask import Flask
from myapp.admin import admin
app = Flask(name)
app.register_module(admin, url_prefix='/admin')

myapp/admin.py
from flask import Module
admin = Module(name)
@admin.route('/')
def index():
return 'This should be at /admin'

[mitsuhiko]

Fixed late binding of url_prefix. This closed by a921aef.