Adding perl, pod2pdf, texinfo as build dependencies.

Building documentation requires /usr/bin/{pod2pdf,pod2texi,pod2hml}.
Making package building idempotent.

Remove .texi, .pdf, and .1 files when cleaning so that:
$ dpkg-buildpackage && pdkg-buildpackage
works.
Remove unnecessary (precompiled) documentation files from the source.

Create target `get-orig-source` to remove precompiled documentation files from
upstream release package.
Log +ds1-1.1 version in debian/changelog.
Removing precompiled documentation files from this git repository.
Credit Michele Orrù for patches to build twice in a row.

We repackage the packages taken from upstream to remove prebuilt
documentation, as a way to bring things a tiny bit closer to reproducible
builds (but not yet there, as timestamps get in the way).

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>