debdiff: Optionally apply 3.0 (quilt) patches before comparison
This is particularly useful when comparing a Debian revision with post-release fixes as patches with a new upstream version in which those fixes have been merged upstream, or when comparing packages that have moved from 1.0 to 3.0 (quilt) source format.
As well as implementing what I requested in #688219, this partially addresses #939602 (but the submitter of #939602 additionally wanted the default to change, which I have not done here).
In addition to the changes being applied to the upstream source code,
the comparison also (somewhat redundantly) includes the changes to
debian/patches. This allows a reviewer to see how any new changes break up
into individual 3.0 (quilt) patches, and an in particular lets a reviewer
see the (hopefully DEP-3) patch descriptions. If this is undesired,
the actual patches can be filtered out with --exclude='*.patch' or by
postprocessing with filterdiff -x.
For those familiar with gbp-pq(1), this is approximately the same
comparison as the one obtained by importing the old and new patch
series with gbp pq import, and then comparing patch-queue/old with
patch-queue/new.
Signed-off-by: Simon McVittie smcv@debian.org
Closes: #688219
/cc @kilobyte