Provide set of URLs as an input file

[witsch]

It'd be very useful to use a set of given URLs for the load test, much like siege's "URL file":

In order to run a regression test or an effective internet simulation, you are going to have to run through the URLs on the server you are testing. To accomplish that, place the URLs in a configuration file.

This makes it possible to collect a realistic set of URL, i.e. from an access log etc, and "replay" them in order to test or ensure performance requirements are still met after some changes.