Merge branch 'maint'

* maint:
  fixup: delete "# serial" line in m4/amversion.in
  news: update about recent ylwrap changes and fixes
  m4: get rid of "# serial" lines
  configure: ${#param} must be supported by the shell for the testsuite
  yacc tests: fix a spurious failure with parallel make
  ylwrap: use proper quoting inside a `...` substitution
  ylwrap: don't uselessly reset the exit status in case of failure
  ylwrap: fix C++ support for Bison
  ylwrap: refactor: move loop invariant
  ylwrap: refactoring: don't rely on the file order
  tests: upgrade and fix Bison test case
  tests: fix bison input file
  ylwrap: comment changes
  ylwrap: modernize idioms
  ylwrap: rename header inclusion in generated parsers
  ylwrap: simplify the list of renamings
  ylwrap: refactor: less duplication

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>