* test/socket/test_unix.rb: 1.9.3 doesn't have IO::EAGAINWaitReadable.
  use IO::WaitReadable instead.  this fixes the test failure introduced
  at r45093.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@45095 b2dd03c8-39d4-4d8f-98ff-823fe69b080e