Known bug with indexes and phi values

[mbellotti]

Need to come back to this later but there's a known bug in indexes when they are using inside any kind of branching logic like so:

increment: func{
        if num.value == 0 {
              num.value = 1;
       else{
              num.value <- num.value[now-1];
       },

index references a variable in the true branch that shouldn't be accessible to the false branch.