Restrict the native generator tests to Node.js v0.11.2.

The v0.11.0 and .1 releases didn't yet support generators.
Add a failing test of unqualified function call receiver objects.

The problem here is that the generated code for the function call looks
like `$ctx.sent(arg)`, so `$ctx` gets used as the receiver for the
function call instead of the global object.

A cute way to fix this would be to emit `(0,$ctx.sent)(arg)` instead.
Fix tests of unqualified function calls added by the previous commit.