[perl6/specs] 582cee: add Pair.exchange as distinct from .invert

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/perl6/specs
  Commit: 582cee8a8c380d4577337136839ee18a991cb941
      
https://github.com/perl6/specs/commit/582cee8a8c380d4577337136839ee18a991cb941
  Author: TimToady <la...@wall.org>
  Date:   2015-02-27 (Fri, 27 Feb 2015)

  Changed paths:
    M S32-setting-library/Containers.pod

  Log Message:
  -----------
  add Pair.exchange as distinct from .invert