Problem: Decision whether message is sent to "more" window is based on
the number of newlines present in a message, rather than the
actual text height.
With the "box" target, messages that come from a cmdline
entered command are not always routed to the more window.
Solution: Still write the message to the target buffer, and calculate
the actual text height. Postpone updating several state
variables until after the decision to re-route is made.
With the "box" target, only consider the text height of the
message if it is not a message from a cmdline entered command.
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