Support IPv6 in address check lookups.

This supports IPv6 in address DNS lookups and socket bind checks. Addresses are
looked up with the system getaddrinfo(), and the v6/v4 preference of this lookup
is respected. IPv6 address literals in the config file are expected to be
bracketed in [], and the result of lookups will be bracketed as well, to support
the ZeroMQ URI format.
Unset the IPV4ONLY socket option if available.

Since IPv6 sockets support both v4 and v6 addresses, the socket option is unset
unconditionally if the parameter is available in the zmq module. The actual
decision as to which address version to use is done by the address lookup code,
which obeys the system v4/v6 preference.
Be more resilient towards missing addresses and hostname lookup failures.
Add a unit test for passing IPv6-formatted addresses to verify_socket.
IPv6 address literals should be specified without brackets in config files.
We're no longer leaking threads. Travis-CI should be OK with 10 worker threads.
tomcat module addition
- tomcat wait function
- tomcat mod_watch funtion
- a bit of docs fix
Merge pull request #4631 from ranl/develop

tomcat module addition
Merge pull request #4632 from s0undt3ch/hotfix/fix-travis-again

We're no longer leaking threads. Travis-CI should be OK with 10 worker threads
Merge pull request #4232 from tohojo/ipv6-support

IPv6 support for master-minion communication
Since turning on ipv6 can break ipv4 in some networks only enable

ipv6 if explicity devind in the config. Also since pyzmq will still
have the flag and then fail silently if the underlying zmq does not support
ipv6
Add extra include docs, fix #4274
Fix #4102

The scheduler was not explicitly calling the returner function
Warn and reset `worker_threads` to the minimum of 3 if lower.