Explicitly pass the type of the operand to fr.makeInterface

I was seeing some panics caused by makeInterface being called with the wrong
type. Rather than try to fix those, I decided to take a step on the long
path of removing the typ field from govalue by passing the value and its
type into makeInterface separately.
Merge pull request #143 from pcc/libgo-mi

Explicitly pass the type of the operand to fr.makeInterface