This patch modifies Root#dispatch() in order to keep the httprequest url
in the current thread's attribute and use if for dumpstacks and the
phantomjs tests remaining requests handling.
Also added a counter in order to avoid looping forever when trying to join unclosed http requests
in phantomjs test suite after a phantomjs failure + added a log.warning in such a case so it's easier to troubleshoot runbot's ir.logging.
Fabien Meghazi