Merge remote-tracking branch 'origin/maint'

Merge remote-tracking branch 'origin/maint'

* origin/maint:
  maint: update gnu-web-doc-update.
  maint: post-release administrivia
  version 2.6
  maint: prepare for release 2.6
  maint: post-release administrivia
  version 2.5.91
  maint: prepare NEWS.
  maint: fix spaces.
  tests: adjust to case where the C compiler is actually a C++ compiler
  tests: fix dependencies
  doc: fix Texinfo command
  maint: Valgrind on OS X.
  tests: be sure that backups are safe.
  maint: dead comment.
  tests: refactor for legibility.
  tests: refactor the bison invocations.
  maint: fix syntax-check ignore patterns.
  gnulib: update
  gnulib: update.
  gnulib: update

Conflicts:
	build-aux/Makefile.am
	cfg.mk
	tests/Makefile.am