Merge branch 'maint'

Merge branch 'maint'

* origin/maint:
  NEWS: warnings with clang
  warnings: avoid warnings from clang
  tests: no longer disable -O compiler options
  yacc.c: initialize yylval in pure-parser mode
  skeletons: style changes
  lalr1.cc: document exception safety
  lalr1.cc: check exception safety of error handling
  lalr1.cc: check (and fix) %printer exception safety
  lalr1.cc: check (and fix) %initial-action exception safety
  lalr1.cc: fix exception safety
  lalr1.cc: check exception safety.
  lalr1.cc: indentation fixes.
  lalr1.cc: don't leave macros define to nothing
  tests: minor improvements
  tests: use $PERL instead of perl
  build: look for Perl in configure.
  tests: fix sed portability issues
  tests: diff -u is not portable

Conflicts:
	data/c.m4
	data/glr.c
	data/lalr1.cc
	data/yacc.c
	doc/Makefile.am
	tests/atlocal.in
	tests/calc.at