Fix repl output after .pseudoToNative changes
Fix repl output after .pseudoToNative changes

In PR #450 Interpreter.prototype.pseudoToNative was modified to make
the JSON.stringify builtin behave more correctly (per ES5.1 spec).

Unfortunately this meant that in repl any expression that yeilded
a function would be shown as having value undefined.

Fix repl so that if the expression evaluates to a function that
function is printed.  (It will still hide methods, as JSON.stringify
does.  But this is better than before, and perfecting repl is not
a priority at the moment.)

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