Overwriting binary files when building a package

[Thomas Weber <tweber@debian.org>]

Hi, 

my upstream ships documentation in PDF format in the normal sources.
Upon build, I re-create those files[1]. The newly generated PDF files
differ from the originally shipped ones. So, I have a problem asserting
that "debian/rules clean" gives me the same source tree as "dpkg-source
-x" which seems to ask for trouble, see 
http://www.mail-archive.com/debian-ocaml-maint@lists.debian.org/msg22803.html
In fact, we already see some issues when using git-buildpackage right
now (currently, I remove the PDF files via dh_clean). 

Is there a way around the "make a backup copy of the original PDF files
and copy it back upon executing 'debian/rules clean'"? And if not, is
there some generic code floating around for doing this (I envision
something like dh_backup ;))?

[1] Part of the documenation for building the PDF is copied from the
source files, so a normal patch to the source code triggers a rebuild of
the documentation - so it's not like I can easily avoid the rebuild of
the PDF files.

Thanks
	Thomas