Restarting stopped zservs

[Ladna]

A while ago, Beast asked if ZDStack restarts crashed zservs. Yes, one
of the things that ZDStack does for you is automatic restarting of
crashed zservs. So say you have the following servers configured:

[ZDCTF 8v8]
# some stuff here

[ZDDL D5M1]
# some more stuff here

[Clan Warz]
# some other stuff

ZDStack checks each of these servers every 500ms. If they're not
running (and they're supposed to be, i.e. they haven't been stopped)
ZDStack restarts them.

This can get you into trouble if you make a mistake in your
configuration. A common mistake is to configure two servers with the
same port, like:

[ZDCTF 8v8]
port = 10666
# some other stuff

[ZDDL D5M1]
port = 10666
# some other stuff

'ZDCTF 8v8' will start first, and then 'ZDDL D5M1' will try to start
and fail, because its port is already in use. ZDStack will detect
that 'ZDDL D5M1' has crashed and restart it... and the server will
crash again... and so on until you figure it out and stop either that
server or ZDStack.

Of course there's a couple things ZDStack could do about that. It
should detect servers with duplicate ports, both during startup and
when the config is reloaded. It should also not start a server more
than a few times a minute -- if a server is repeatedly crashing it
should stop the server and log an error message. Both of these things
are relatively easy to add and will be included in 0.11.