* Merge from Debian unstable. Remaining changes: - Allow -fstack-protector on arm64 now that GCC and glibc support it. - Change native source version/format mismatch errors into warnings until the dust settles on Debian bug 737634 about override options. - Add DPKG_UNTRANSLATED_MESSAGES environment check so that higher-level tools can get untranslated dpkg terminal log messages while at the same time having translated debconf prompts. - Special-case arm{el,hf} ELF objects in Shlibs/Objdump.pm for multilib. - Map unqualified package names of multiarch-same packages to the native arch instead of throwing an error, so that we don't break on upgrade when there are unqualified names stored in the dpkg trigger database. - Add logic to the postinst to `dpkg --add-architecture i386' on new installs on amd64, mimicking our previous behaviour with the conffile. - Apply a workaround from mvo to consider RC packages as multiarch, during the dpkg consistency checks. (see LP: 1015567 and 1057367). * Drop obsolete migration code and guards from pre-trusty dpkg versions.