replace psyntax's syntax-error with r6rs' syntax-violation

replace psyntax's syntax-error with r6rs' syntax-violation

* module/ice-9/boot-9.scm (syntax-violation): Well, as long as we have to
  have a function for indicating syntax errors, let's let it be a
  well-thought-out one -- syntax-violation from r6rs. No more
  syntax-error.

* module/ice-9/psyntax-pp.scm: Regenerated.

* module/ice-9/psyntax.scm: Replace instances of syntax-error with
  syntax-violation. Implement as a scm-error to 'syntax-error, with some
  nice arguments.