bug#6085: Eshell doesn't handle ANSI escapes/colors well

[Chong Yidong]

>> Eshell doesn't handle a terminal escape code like ^[.
>>
>> [~/emacs.20100501/lisp/eshell]$ export TERM=xterm-256color
>> [~/emacs.20100501/lisp/eshell]$ *grep --color=auto ansi esh-*
>> ^[[Kesh-mode.el^[[K^[[K:^[[K    eshell-handle-^[[Kansi^[[K-color
>
> This was working some time ago so maybe looking at what have changed and
> reenable this feature should be good.

No, this is not a regression.  The mess here is due to the ^[[K ("erase
line") sequence that colorized grep emits.  (I don't know why it needs
this control sequence.)

There is no sane way for the ansi-color package to handle this.  Unlike
term.el, it is not intended to be a terminal emulator.  The best we can
do is to delete such sequences from the output, and I've committed a
change to do that.