define macros before functions using macros; more MV fixen in srfi-69

define macros before functions using macros; more MV fixen in srfi-69

* module/srfi/srfi-69.scm: Move the macros up before the functions that
  use them, so that the compiler can do its job.
  (hash-table-walk): While it is true about what I said about R5RS
  before, it seems that for R6 this will have to change. Anyway. In the
  meantime, since the test suite checks that hash-table-walk procedures'
  return values and number of return values are ignored, call that
  procedure within a call-with-values.