Add http_listener structure

Keeps track of webroots on a per-listener basis. Modified inet_listener() to
return a pointer to the listener object. The web listener keeps a pointer to
the default webroot. All http-conns keep a pointer to the web listener object.

Eventually each listener will keep a map of all the vhosts and such and
point to different webroot objects.
WIP: Add inotify
Support TCP_FASTOPEN
Merge branch 'master' into vhost

Conflicts:
	httpd.c
	nbio-listener.c
Complete nbio API

It allows watches to be added, but doesn't yet allow for removal.
We don't really need that right now anyway.
Split httpd.c in to http_conn.c

Keeps things nicely separated but also paves the way for adding
different protocols at some later date if we become beset with
the curse of feeping creaturism.
Add stubbed out vhost management routines

Scan the vhosts dir at startup and watch it with inotify calling
vhost_add()/vhost_del() where appropriate.
Silence compiler warning
Add crit-bit trees, to be used for vhost maps
critbit: Change API to allow handling of value pointers

When inserting an item take a triple-indirect pointer which stores
a pointer to the value-pointer. The caller can check for NULL to
see if an item was already allocated there and decide what to
assign to it.

For delete, take a double-indirect pointer which returns the
value of the deleted item.

For search, take a double-indirect pointer which holds the pointer
to the found nodes value so that it can be examined or updated.

For delete, take a callback function which gets passed the
value pointers of all the deleted nodes.

All of the value manipulation stuff is optional, pass NULL
if you don't care about the map values.
Maintain data map of vhosts to webroot objects
Split out vhosts code out and give it an interface
Fix error condition for close()
Few notes about requirements
inotify: Woops, properly set inactive state on EAGAIN
Add vhosts support
Unref webroots on http connection teardown.

Also, I think fix a leak of httpd conns? Cannot be true?! :)