zshrc: New prompt: Fix quoting style in dumb-terminal config

Signed-off-by: Frank Terbeck <ft@grml.org>
zshrc: New prompt: Handle grml-chroot in dumb-terminal config

Signed-off-by: Frank Terbeck <ft@grml.org>
zshrc: New prompt: Enable one of the prompts

Mimic the old way of choosing the "right" prompt.

Signed-off-by: Frank Terbeck <ft@grml.org>
zshrc: New prompt: Provide fallback in case promptinit fails

This should not happen usually. But better be safe than sorry.

In case something goes wrong we only support _one_ prompt, with the original
root-is-red changeroo.  This is good enough as a fallback.

Signed-off-by: Frank Terbeck <ft@grml.org>
zshrc: New prompt: Remove old prompt setting scheme

Signed-off-by: Frank Terbeck <ft@grml.org>
zshrc: New prompt: Reorganise the prompt section

Signed-off-by: Frank Terbeck <ft@grml.org>