Use a Holder for contain (value) and make sure it takes an Equality. Had to fix some
type params here and there, and add implicits for Holder and Holder with Equality. I broke
a stack depth, so two tests are failing. Will leave that for Chee Seng.


git-svn-id: http://scalatest.googlecode.com/svn/trunk@5135 fd1274fd-080f-5963-8033-43ee40fcd1de