Bug#2656: ld.so maintainer scripts not idempotent

[Ian Jackson <ian@chiark.chu.cam.ac.uk>]

Package: ld.so
Version: 1.7.14-2

Matt Linden writes ("Bug#2654: libc5 predependancy on ld.so1.7.14-2"):
...
> dpkg: error processing ld.so-1.7.14-2.deb (--install):
>  trying to overwrite `/usr/include/dlfcn.h', which is also in package libc
> Expect some cache has wrong version warnings if upgrading
> to version 1.7.x for the first time.
> mv: `ld.so.1.7.10' and `ld.so' are the same file
> mv: `ld-linux.so.1.7.10' and `ld-linux.so.1' are the same file
> Errors were encountered while processing:
>  ld.so-1.7.14-2.deb

The messages from `mv' are (presumably) from the ld.so preinst or
postinst script, which dpkg is running as part of the error recovery.

The problem here is that the scripts are not idempotent.  Please see
the latest Guidelines, which have an appendix which describes exactly
in what order and when maintainer scripts can be executed.

Maintainer scripts should not fail just because they've already been
run, because if they do then certain kinds of error become
irrecoverable.

Ian.