Raise NotImplementedError for .evalf() on indefinite integrals.

Fixes issue 3808: Calling .evalf() on indefinite integral throws an exception
http://code.google.com/p/sympy/issues/detail?id=3808
Remove superfluous check for tuple instance.

Limits are canonicalized to tuples by the constructor.
Merge pull request #2084 from jrioux/evalf

Raise NotImplementedError for .evalf() on indefinite integrals.