Missing IPv6 ORPort reachability check

Issue: Tor does not log (or does not perform) a test to determine if an IPv6 ORPort is reachable.

Tor does log a corresponding test for an IPv4 ORPort.

Environment: Debian squeeze amd64, latest patches Tor version 0.2.4.2-alpha (git-0537dc6364594474)

How to reproduce:

configure Tor with both IPv4 and IPv6 IP addresses and OrPorts.
start Tor
the Tor log file will show a test to determine if the IPv4 OrPort is reachable, but not if the IPv6 ORPort is reachable.
(this particular system was configured as a bridge)

Expected Behavior: The user might expect to see a log entry for IPv6 that corresponds to the following log entry for IPv4:

"Sep 22 11:09:21.000 [notice] Now checking whether ORPort [host's IPv4 address]:443 is reachable... (this may take up to 20 minutes -- look for log messages indicating success)"

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