Merge branch 'maint'

* maint:
  tests: prefer using 'is_newest' over 'ls -t' hacks
  tests: implement is_newest as an auxiliary script, not shell function
  tests: fix some spurious failures in VPATH setup
  tests: work in VPATH setup again

diff --cc Makefile.am
Simple merge

diff --cc defs
Simple merge

diff --cc syntax-checks.mk
Simple merge

diff --cc t/ax/test-init.sh
Simple merge