release: Use full window size for installer over serial lines

[jrtc27]

Summary

When running over a serial line we end up defaulting to 80x24, which is
rather cramped for many dialog boxes and occupies very little screen
space for most modern terminals. Thus, run resizewin -z to set the
terminal size if not already known before starting the installer, just
as we do for csh and sh login shells already in their default dotfiles.

[jrtc27]

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[jrtc27]

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[jrtc27]

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[jhb]

This has timed out at this point.

[gjb]

In D34414#796320, @jhb wrote:

This has timed out at this point.

Sorry, it has indeed. @jrtc27 apologies for the oversight.