* Fixes pipelining which broke in 20120422 as a result of the virtual host
config changes. An additional configuration step gets added. You now need
to create a 0-length "vhost.ip-address" file in addition to everything
else, in order to enable virtual configuration for this ip-address. This
needs to be done explicitly, in order to avoid breaking pipelining.
* Also this also adds a alternative, slightly limited, form of virtual
configuration based on a message's return address. Creating a
"vhost.domain" configuration file enables virtual configuration for
messages with "@domain" return address. The courier(8) man page is updated
with more information and details.