Update to new upstream release 1.43.6.

This fixes FreeBSD-related regressions observed in 1.43.4 and 1.43.5,
and portability issues around quota support on 32-bit builds.

Changelog: http://e2fsprogs.sourceforge.net/e2fsprogs-release.html#1.43.6

[The MFH request will also need to take 1.43.5 upgrades into account,
so the easiest would probably to merge the entire history since branching.]

MFH: 2017Q3