The Debian Policy states that a branch can and should specified in
Vcs-Git if the packaging bits are not in the default branch, see
https://www.debian.org/doc/debian-policy/ch-controlfields.html#version-control-system-vcs-fields

When putting options in debian/source/options the leading "--" must be
stripped.

This fixes a warning from `cme check dpkg`:

Warning: source options '--extend-diff-ignore' is confusingly close to 'extend-diff-ignore' (edit distance is 2). Is there a typo ?

Debian revisions should be stripped from versions in symbols files.

Not doing so leads to dependencies unsatisfiable by backports (1.0-1~bpo
<< 1.0-1 while 1.0-1~bpo >= 1.0).

This fixes the following lintian error:

E: libgrokj2k1: symbols-file-contains-current-version-with-debian-revision on symbol _ZNKSt13__future_base13_State_baseV221_M_is_deferred_futureEv@Base and 351 others

Add a repository-specific configuration file for git-buildpackage to
avoid having to pass options to it every time gbp is run.

This reverts commit 10fc5402.

fixes #332

Thanks to George Cho for coming up with a fix.
https://www.swig.org/Doc4.0/Perl5.html#Perl5_nn9