#209 shttp: port allocation failure is fatal

[Manuel Moos]

When shttp fails to allocate the configured port, it
just terminates the program. This makes problems on
playback (already fixed by not starting the web
server), but also during testing: "make devcheck"
starts a server for testing purposes, and if another
server is already running, the test fails. This can be
worked around by giving the servers different ports to
bind to using settings_web.cfg, of course, so it's not
critical.