Matt Harbison <matt_harbison@yahoo.com> [Sat, 10 Nov 2018 23:54:46 -0500] rev 4254
compat: drop Mercurial 4.3 support for exthelper
The last release email noted plans to drop 4.3 and 4.4 support in the next
feature release. I'd like to move this code into core, and dropping this should
allow the class to be copied in unmodified.