Merge branch 'master' into ng/master

Merge branch 'master' into ng/master

* master:
  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
  tests: automatic re-execution works for non-POSIX shells too
  tests: use more POSIX shell features our test scripts
  docs: avoid failures with development version of Texinfo (4.13.90)
  typofix: s/test derivers/test drivers/ in check.am comments
  typofix: s/env/even/ in comments in GNUmakefile

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>