#174 lvar with same name as prim doesn't work right

[Torne Wuff]

I'm trying to make Triggur's TerraForm work on Proto
and have encountered a Proto bug =)

If you define a variable (or lvar) with the same name
as a primitive (TerraForm uses 'nextroom' as an lvar)
then any reference to that variable will call the prim
instead. This makes rather random seeming bugs. =)

Either the variable should override the primitive
(probably a bad idea) or it should be an error to
declare a variable with the same name as a primitive.