Merge branch 'maint'

* maint:
  maintcheck: fix failures, both real and spurious
  subdir tests: avoid an use of "make -j4", for portability
  tests: avoid failure due to libtool quirks in C++ demo test
  tests: fix spurious failures due to missing '$sleep'
  subdirs: unify rules for "cleaning" and "normal" recursive targets
  tests: add a "demo" test on C support
  tests: look for '.lo' rather than '.o' object when using Libtool with C++
  cosmetics: few typofixes in older ChangeLogs, suggested by "codespell.py"
  maint: grammar fixes: s/all these/all of these/
  subdir-objects: improve "make mostlyclean" efficiency and flexibility

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

diff --cc NEWS
Simple merge

diff --cc automake.in
Simple merge

diff --cc doc/automake.texi
Simple merge

diff --cc syntax-checks.mk
Simple merge

diff --cc t/list-of-tests.mk
Simple merge