DoS under Debian/apache2-mpm-itk #355

What steps will reproduce the problem?
1. Install all requisites.
2. Let visitors use your site as they usually do.
3. See many stalled apache processes and DoS in the end.

What is the expected output? What do you see instead?

Lots of stalled apache processes roughly equivalent to the number of requests 
to mod_pagespeed's handled files.

What version of the product are you using (please check X-Mod-Pagespeed
header)?

mod-pagespeed-beta 0.10.19.3-r1179

On what operating system?

Debian Linux amd64

Which version of Apache?

2.2.16-6+squeeze4

Which MPM?

apache2-mpm-itk

Please provide any additional information below, especially a URL or an
HTML file that exhibits the problem.

Downgrading to 0.9.18.7-r900 solves the problem.