Merge remote-tracking branch 'origin/maint'

Merge remote-tracking branch 'origin/maint'

* origin/maint: (22 commits)
  tests: ignore code coverage/profiling failure messages
  doc: fix some invalid @ref.
  build: fix previous commit.
  install-pdf: fix.
  NEWS: Update.
  %printer: support both yyo and yyoutput.
  doc: mfcalc: demonstrate %printer.
  tests: style changes.
  build: require Flex.
  build: flex.m4: check for Flex.
  build: flex.m4: quote properly.
  build: flex.m4.
  build: autoconf: update.
  glr: eliminate last bits of unwanted locations.
  NEWS: 2.6 will drop K&R.
  TODO: remove dead items.
  TODO: import from master.
  gnulib: update.
  maint: update NEWS.
  doc: fix index.
  doc: fix documentation of YYERROR.
  c++: more YY_NULL

Conflicts:
	TODO
	bootstrap
	data/c.m4
	data/glr.c
	data/lalr1.cc
	doc/bison.texinfo