* Andreas Tille <andreas@an3as.eu>, 2016-06-27, 12:41:
dh_autoreconf autoheader: warning: missing template: EASEL_COPYRIGHT autoheader: Use AC_DEFINE([EASEL_COPYRIGHT], [], [Description])
Normally one would fix such errors by adding third argument (description) to all instanced of AC_DEFINE(_UNQUOTED) where it was missing.
But in this case upstream doesn't seem to be using autoheader at all; their header template (easel/esl_config.h.in) looks manually-crafted. So you should probably just ask autoreconf not to call autoheader:
AUTOHEADER=true dh_autoreconf
-- Jakub Wilk