bug#490: 23.0.60; color-theme breaks input in *shell* buffer

[Glenn Morris]

> Downloaded color-theme from http://download.gna.org/color-theme/
> (and added the directory to the load path and compiled the elc)
>
> If I then start a freshly built emacs from cvs and 
> M-x shell
> M-x load-library color-theme
> M-x color-theme-select
> select a theme and then click the quit 'button'
> which takes you back to *shell* typing pwd (or indeed anything) 
> at a shell prompt (and return) will produce no output and an error
> message in the echo area:
>
> comint-snapshot-last-prompt: Wrong type argument: integer-or-marker-p, nil
>
> where it is attempting:
>
>   add-text-properties(nil nil (font-lock-face comint-highlight-prompt))

This is a bug in color-theme.

color-theme-install-at-point is stomping over all the overlays in a
buffer. It should be more careful about which buffer it is in, and
should restrict itself to goto-address overlays, eg by using
goto-address-unfontify.