added doc for should_change taking a block
added doc for should_change taking a block

git-svn-id: f1a1267e29db6ed751edc5bdb54cf7d87c16124a@1208 410327ef-2207-0410-a325-f78bbcb22a5a

chip/rspec-tmbundle,dchelimsky/rspec,patmaddox/rspec2rails2,patmaddox/rspec,graaff/rspec,dchelimsky/rspec-stories,rspec/rspec.tmbundle,dchelimsky/rspec,alitalia/rspec,rspec/rspec.tmbundle,infininight/rspec-tmbundle,weplay/rspec-rails,phinze/rspec,drnic/rspec-rails,die-antwort/rspec-tmbundle,dchelimsky/rspec-stories,patmaddox/rspec,dchelimsky/rspec-rails,die-antwort/rspec-tmbundle,infininight/rspec-tmbundle,mcmire/rspec-rails,mrkn/rspec,alitalia/rspec