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Remove prev_(fkey|keytran}_(map|start|end) since we don't want to pass
things through those maps after downcasing events.
Enforce that keytran_end <= fkey_start, i.e. that key-translation-map
applies after function-key-map.
Make sure that keytran can be done in the middle in the sequence.
Be careful not to throw away events past the one we downcase.