Merge branch 'branch-2.6' into maint

Merge branch 'branch-2.6' into maint

* origin/branch-2.6:
  regen
  yacc.c: do not define location support when not using locations
  maint: be compilable with GCC 4.0
  tests: address a warning from GCC 4.4
  tests: don't use options that Clang does not support
  tests: restore the tests on -Werror
  regen
  parse-gram: update the Bison interface
  fix comment