Bug#574729: apt pinning doesn't work for essential packages

[Teodor MICU <mteodor@gmail.com>]

reopen 177952
found 177952 0.7.20.2+lenny1
fixed 177952 0.7.25.3
thanks

The main point of these old bug reports is that there is no way of
(willingly) preventing the installation of an essential package.
In our present time we're confronting with the 'diff' -> 'diffutils'
transition of an essential package. I have to keep "testing" in my
sources.list file for a single 'noarch' package (PHP-based
application) that I want to keep it updated. I have no reason to
replace 'diff' with 'diffutils' because of this, so I'm looking for a
solution of preventing an accidental install of 'diffutils' essential
package.

> You can prevent the installation of new essential packages by
> pinning them to -1:
>
> 	Package: test-essential
> 	Pin: version 0.0-0
> 	Pin-Priority: -1
>
> Thus I'm also closing bug #177952; because it is possible
> to "suppress installation of essential packages". Due to
> Bug #216768 this may not always work in practice; but I
> have not checked it further.

That's the thing, not even using "Pin-Priority: -1" for an essential
package will prevent it from being installed. Either by executing
"apt-get dist-upgrade" or "apt-get install diffutils" the new
essential package is installed even if the pin priority is "-1".

This bug seems fixed for 'squeeze' but not on 'lenny'. Does a fix for
this qualifies for an update or will be tagged with lenny-ignore?

Thanks