repl mode order of cells

[tlienart]

Actually this causes a problematic issue:

```>
a = 5
b = 2;
a + b

a = 1//2

first pass will be fine, then simply update `b = 2` and the `a` that gets used is... `1//2`.

[tlienart]

this is specific to repl mode because each line is executed as its own cell but, in fact, if anything changes in that, there should be a force reeval.