Performance penalty for large pages

[jkuczm]

When PhasedRenderMiddleware is turned on, rendering time grows very fast with size of the content that is outside of phased block.

For simple page that results in ~100 kB of HTML:

• without PhasedRenderMiddleware in MIDDLEWARE_CLASSES is rendered below 0.1 second
• with PhasedRenderMiddleware it takes over 20 seconds on my machine to render.

This slowdown is reproducible in many environments:

• devserver; python 2.7.3; django 1.4.6, 1.5.2
• apache 2.2.22; mod_wsgi 3.3; python 2.7.3; django 1.5.2
• apache 2.2.15; mod_wsgi 3.2; python 2.6.6; django 1.5.2

Steps to reproduce this problem:

1. setup example project from django-phased repository
2. add long text to base.html template, outside phased block
   e.g. {% for _ in ""|ljust:"10000" %} some text {% endfor %} just after <div id="body">
3. visit any page using base.html template e.g. /blog/
4. wait for page to appear