Intercept the input in comint-mode.  This can be used to run eshell
command, or run some command in a terminal buffer from the command
line in shell buffer.  That is, this is to combine the best part of
shell, eshell and term mode.  For example, you can run eshell
`grep' in the shell buffer, or when you run `top' in the shell
buffer, a terminal buffer is poped to run it.  SSH is supported to
run command remotely.