Shell mode: suggest adding newline when carriage return printed

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In XEmacs 21.1 (patch 8) "Bryce Canyon" [Lucid] (i386-redhat-linux) of Mon Feb 14 2000 on porky.devel.redhat.com
configured using `configure i386-redhat-linux --with-gnu-make --with-gpm=no --with-sound=none --with-pop --mail-locking=flock --with-clash-detection --debug=no --error-checking=none --prefix=/usr --lockdir=/var/lock/xemacs --with-x11 --with-dialogs=athena3d --with-scrollbars=lucid --with-menubars=lucid --with-xpm --with-mule=no --dynamic=yes --with-tty=yes --with-ncurses'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Some programs try to produce a pretty display by printing carriage
return (^M) and overwriting the current line.  In XEmacs's shell mode,
however, the carriage return is printed as ^M with no new line
started, so the display comes out looking like

^M                                                                             ^Mt/test_filters....ok 1/60^M                                                                             ^Mt/test_filters....ok 2/60^M                                                                             ^Mt/test_filters....ok 3/60^M

The intended effect is a moving counter that changes from 1/60 to 2/60
and so on, but in a shell buffer it comes out as one long line with
control characters.

Perhaps the bug is with the program that produces the carriage returns
- perhaps it should check the value of $TERM before printing such
strange characters.  This would certainly be true if it were using
ANSI escape sequences for colours or cursor positioning or other
strange things.  But I don't think it's the case here; CR is an ASCII
standard character after all, and it's not unreasonable for a program
to print it and expect its terminal to do something sensible.

Suggested fix is for M-x shell to start a new line after each solitary
CR character.  Then the output from the command would look like

^M
                                                                             ^M
t/test_filters....ok 1/60^M
                                                                             ^M
t/test_filters....ok 2/60^M
                                                                             ^M
t/test_filters....ok 3/60^M

which, while not as cute as a real terminal, is readable.

Recent keystrokes:

ESC O C ESC O C ESC O C ESC O C ESC O C ESC O C C-g 
C-x k RET d a t e SPC - - v e t r s DEL DEL DEL r s 
i o n RET C-x b RET T Z = B S T SPC m a k e SPC t e 
s t RET ESC x r e p o r t - x e m a c s - b u g RET 
DEL DEL DEL DEL DEL DEL DEL DEL DEL DEL e m SPC b u 
SPC RET


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