Don't throw a ServerSetupException for interrupted system calls; they happen
a lot when the epoll file descriptor sets are modified.
Use the thread++ mutex implementation.
Split the expiration of old connections out of the central handling code and
do them asynchronously. Make sure whoever accesses the connection list owns
it.
If a connection is shut down, declare it to be at the end of file.
Forward IsShutdown to the acknowledgement decorator.
Also forward IsShutdown in the LineBufferDecorator.