Merge remote-tracking branch 'origin/maint'

* origin/maint:
  news: prepare for forthcoming release
  doc: explain how mid-rule actions are translated
  error: use better locations for unused midrule values
  doc: various minor improvements and fixes
  tests: ignore more useless compiler warnings
  tests: be robust to C being compiled with a C++11 compiler
  build: beware of Clang++ not supporting POSIXLY_CORRECT
  maint: post-release administrivia
  version 2.6.90
  build: fix syntax-check error.
  cpp: simplify the Flex version checking macro
  news: improve the carets example and fix a typo
  cpp: improve the Flex version checking macro
  carets: improve the code
  maint: update news
  build: keep -Wmissing-declarations and -Wmissing-prototypes for modern GCCs
  build: drop -Wcast-qual
  gnulib: update

Conflicts:
	NEWS
	doc/Makefile.am
	doc/bison.texi
	gnulib
	src/reader.c
	tests/actions.at
	tests/atlocal.in
	tests/input.at