Use reflect api type conversion to assign value in nodeutil

[HRogge]

Using the conversion function of the go reflect API allows nodeutil.reflect to assign values derived from go basic types e.g.

type MyString string

[HRogge]

I have added a second commit that adds the logic to convert a leaflist and throws a proper error (instead of a panic) if types are not convertible.

[dhubler]

looks great