Add "Xen mode" in capture.
Add "Xen mode" in capture.

With "-X <domname>" capture will track what pty is being exposed by
xenconsoled for a domU console. Capture will doggedly reconnect whenever
it gets disconnected from the pty (which happens during reboots, etc.)

Capture can even be started before the domain exists and it will keep
trying til it does. So betware of typo-ing the domain name, capture won't
care!

Also added "-R <retry-interval-in-ms>" option to determine capture's
"doggedness"--how often it will retry to establish a connection in the
remote/program/xen modes.

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