Disallow second_derivative and hessian functions to be called without g

Currently, `derivative.jl` has the two following definintions

``` .jl
second_derivative(f::Function) = second_derivative(f, derivative(f), :scalar, :central)
hessian(f::Function) = second_derivative(f, gradient(f), :vector, :central)
```

however we discussed that by estimating the first derivative to hand to the second derivative is error prone and subject to possibly large round off error.

I think it's simple enough for a user to input `second_derivavitve(f,derivative(f))` explicitly if they want to take this risk.

Thoughts?
@johnmyleswhite