AnyEvent::Util::run_cmd behaves badly on Windows

Any of the code in the qtqa module which calls AnyEvent::Util::run_cmd tends to crash or otherwise behave badly on our Windows test machines.

Currently this includes:

• QtQA::Gerrit module
• qt-jenkins-integrator.pl
• one change https://codereview.qt-project.org/31422 abandoned due to this issue

The AnyEvent author suggested it may be a problem with the perl implementation - http://lists.schmorp.de/pipermail/anyevent/2012q3/000366.html

It would be good to investigate further and fix or work around this, or if not possible, explicitly document all the affected code which can't be safely used on Windows.

This is low priority since none of this code is particularly needed to run on Windows at the moment, but it should be kept in mind not to introduce further dependencies on AnyEvent::Util::run_cmd on code which needs to run on Windows.