Bug#562863: Extend description of filesystem namespace clashes

[Guillem Jover <guillem@debian.org>]

Package: debian-policy
Version: 3.8.3.0

In the first paragraph in §10.1 (Binaries), there's a description of
when is and is not appropriate to have a filename clash for binaries,
and what to do if such situation arises.

I think this needs to be extended and generalized to include several
other cases, maybe refactoring the information into other sections and
making this one a reference to them. The points I think need mentioning
are:

 * This should apply to any public interfaces, not just binaries, as
   similar problemes arise with incompatible or completely distinct
   functionality being exposed through the same pathname. Those would
   include among others: header files, shared/static libraries,
   plugins, interpreter modules, etc.

 * Make explicit it's not acceptable to move a conflicting binary into
   another directory in the PATH, as that does not actually solve the
   filename clash, it just shadows it. (This might already be implied
   by the fact that it talks about filenames instead of pathnames, but
   making it more clear seems important to me.)

 * It's not acceptable to use Replaces or diversions either to get out
   of such situation. I guess this one is obvious, but I think it's
   worth including even if just in passing in a parenthetical like the
   references to alternatives and Conflicts in §10.1.

If there's agreement on this, I might try to provide some wording at
some point if no one else has done that already by then.

regards,
guillem