mod_firehose: Add a new debugging module able to record traffic passing through the server in such a way that connections and/or requests be reconstructed and replayed.

Warning in configure -h that mod_dumpio was only for developers and testing was erroneous.

Add to modules' help text (displayed by ./configure -h) more information that will be useful in deciding whether to enable them or not.

This tree can't be named modules/debug/. Now it isn't.