bug#28326: exiv2 0.26 hash mismatch

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

tl;dr: exiv2 source archive was updated in-place and the verification
below gives us confidence that we can safely update the hash.

On current master, the following happens:

$ guix build exiv2

Starting download of /gnu/store/jcapi6vk4a14hch5jgsh5zps958g91sb-exiv2-0.26-trunk.tar.gz
From http://www.exiv2.org/builds/exiv2-0.26-trunk.tar.gz...

[...]

sha256 hash mismatch for output path `/gnu/store/jcapi6vk4a14hch5jgsh5zps958g91sb-exiv2-0.26-trunk.tar.gz'
  expected: 1hsdzlzgkipprqh93yj81mrckl2l7c2mn2i84691pallnjz5qqhc
  actual:   1yza317qxd8yshvqnay164imm0ks7cvij8y8j86p1gqi1153qpn7

Looking at what happened at the source obtained through the Wayback
Machine at the time it was last updated in Guix[1] compared to now[2], we see
that:

1. The project maintainers updated the MD5 and filesize of the file
"exiv2-0.26-trunk.tar.gz", which name and URL remained unchanged.

Let's validate those weak MD5 hashes:

$ md5sum exiv2-0.26-trunk.tar.gz  # old one
f936d2ca5cbe1e18c71ca2baa5e84fb4  exiv2-0.26-trunk.tar.gz

$ md5sum exiv2-0.26-trunk\(1\).tar.gz  # new one
5399e3b570d7f9205f0e76d47582da4c  exiv2-0.26-trunk(1).tar.gz

OK, at least the advertized signature validates.

2. When extracting those two archives and diffing them, we see the changes:

$ diff -ur exiv2-trunk-old/ exiv2-trunk-new/
Only in exiv2-trunk-old/: ._AUTHORS
Only in exiv2-trunk-old/: ._bootstrap.macports
Only in exiv2-trunk-old/: ._bootstrap.mxe
Only in exiv2-trunk-old/: ._CMakeLists.txt
Only in exiv2-trunk-old/: ._CMake_msvc.txt
Only in exiv2-trunk-old/config: ._aclocal.m4
Only in exiv2-trunk-old/config: ._CMakeChecks.txt
[...]
Only in exiv2-trunk-old/xmpsdk/src: ._XMPMeta-Serialize.cpp
Only in exiv2-trunk-old/xmpsdk/src: ._XMPUtils.cpp
Only in exiv2-trunk-old/xmpsdk/src: ._XMPUtils-FileInfo.cpp
Only in exiv2-trunk-old/xmpsdk/src: ._XMPUtils.hpp
Only in exiv2-trunk-old/xmpsdk: ._src
Only in exiv2-trunk-old/: ._xmpsdk

A pretty harmless cleanup. Still, the practice of updating a release in
place is not very good... Upon further digging, the issue was already
reported and discussed[3][4].

Note: they are moving to Github and in the furure the releases will be
offered directly through Github.

Patch will follow.

[1] https://web.archive.org/web/20170606065325/http://exiv2.org/download.html
[2] http://exiv2.org/download.html
[3] http://dev.exiv2.org/issues/1299
[4] https://github.com/Exiv2/exiv2/issues/19