Set up for output redirection.
This function sets local variables that are used by `comint-redirect-filter'
to perform redirection.
Output from COMINT-BUFFER is redirected to OUTPUT-BUFFER, until something
in the output matches FINISHED-REGEXP.
If optional argument ECHO-INPUT is non-nil, output is echoed to the
original Comint buffer.
This function is called by `comint-redirect-send-command-to-process',
and does not normally need to be invoked by the end user or programmer.
(fn OUTPUT-BUFFER COMINT-BUFFER FINISHED-REGEXP &optional ECHO-INPUT)