If non-nil, expand input command history references on completion.
This mirrors the optional behavior of tcsh (its autoexpand and histlist).
If the value is `input', then the expansion is seen on input.
If the value is `history', then the expansion is only when inserting
into the buffer's input ring. See also `comint-magic-space' and
`comint-dynamic-complete'.
This variable is buffer-local.