Tramp over su, with odd zsh prompt

[Stefan Monnier <monnier@iro.umontreal.ca>]

I recently tried to use Tramp to access a file via `su' and bumped into the
following problem: the prompt (resulting from a very plain default setting
PS1="%m%# ") looks like

    %<78 SPC>^M^Malfajor% 

where alfajor is the machine name (an argentine pastry).

So it seems that although Tramp sets TERM=dump, the `zsh' executable
(version 4.3.2, from Debian testing) uses funny carriaqe-return trickery and
for apparently no good reason.

Has anybody seen this before?  Should I just set
tramp-shell-prompt-pattern accordingly?  Have you heard of such
behavior already (and maybe some way to get zsh to behave a bit better)?


        Stefan