bug#28500: 25.3; shell mode starts echoing command

[Glenn Morris]

Barry A. Warsaw wrote:

> * M-x shell RET
> * Go to the shell and type `ls RET`
> * See the output of the `ls` but *not* the actual `ls` command
> * Enter an interpreter; two choices which reproduce the problem include 
> `sqlite3` and `python3`
>   Type `sqlite3` at the shell prompt
> * Type .exit at the sqlite3 prompt (notice that the `.exit` was echo'd
>   before the shell prompt came back; the bug is now active
> * Type `ls RET` at the shell prompt.  Notice that the `ls RET` was
>   echoed before the ls output was printed.

FWIW, I cannot reproduce this on RHEL7.