RF: Constraints are now in place in all uses of the Parameter class
(obtained by converting the textual description from allowedtype keyword)
Merge branch 'master' of https://github.com/PyMVPA/PyMVPA into constraints
NF+BF: Added EnsureTupleOf to handle tuples
Merge pull request #214 from neurosbh/constraints

RF: Constraints are now in place in all uses of the Parameter class