This is a workaround for bind failing with EINVAL sometimes on OSX.
I don't know why; EVINAL should mean the socket is already bound to an
address, but this is with a new socket.
The webapp can only run on one of ipv4 and ipv6, no both. Some web browsers
may not support ipv6, so ipv4 is the safe choice.
The actual problem I ran into with it only listening to ipv6 was that
Utility.Url.exists was failing to connect to it. I doubt that haskell's
HTTP library is ipv4 only. More likely, it was only trying one address,
and tried ipv4 first.
To avoid conflict with different liftIO from MonadIO (in some version of
yesod not the one I have here), and because it's generally clearer, since
this module has both Wai and Yesod stuff, to qualify them both.
Old 1.0.1 version is still supported as well. Cabal autodetects
which version is available, but in the Makefile, WITH_OLD_YESOD
has to be configured appropriately.
I have not squashed all the $newline warnings with the new Yesod.
They should go away eventually anyway as Yesod moves past that transition.
This avoids forking another process, avoids polling, fixes a race,
and avoids a rare forkProcess thread hang that I saw once time
when starting the webapp.
