Most of the changes this time are preparation for future
new features and optimizations, that hasn't yet been well
tested and polished.

However, we have several new features. The most important
one is the --tcp-close option to help migration of Docker
containers, that constantly change their IP address.

And, as usually, a set of bugfixes.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>