Bug#820816: stop using gnulib

[Antoine Beaupré]

Source: libidn
Severity: normal

the use of gnulib in this package makes it significantly harder to
backport security patches around the different Debian suites. I have
spent a long time trying to figure out how to update the gnulib source
code in libidn for CVE-2015-2059, for example. it was pretty painful!

using an external library like libunistring would be much better. i
understand that gnulib is necessary to port to certain environments
for the GNU system, but this here is Debian, we can certainly do
better!

this would also be in accordance with §4.13:

https://www.debian.org/doc/debian-policy/ch-source.html#s-embeddedfiles

-- System Information:
Debian Release: 8.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500, 
'stable'), (1, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 4.2.0-0.bpo.1-amd64 (SMP w/2 CPU cores)
Locale: LANG=fr_CA.UTF-8, LC_CTYPE=fr_CA.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)