Expand input command history references before point.
Expansion is dependent on the value of `comint-input-autoexpand'.
This function depends on the buffer's idea of the input history, which may not
match the command interpreter's idea, assuming it has one.
Assumes history syntax is like typical Un*x shells'. However, since Emacs
cannot know the interpreter's idea of input line numbers, assuming it has one,
it cannot expand absolute input line number references.
If the optional argument SILENT is non-nil, never complain
even if history reference seems erroneous.
If the optional argument START is non-nil, that specifies the
start of the text to scan for history references, rather
than the logical beginning of line.
See `comint-magic-space' and `comint-replace-by-expanded-history-before-point'. Returns t if successful. (fn &optional SILENT START)