`export {...}` doesn't work with ES6 target and non-ES6 modules

[ahejlsberg]

In #4811 we enabled generating code for ES6 with non-ES6 modules (which, for example, is useful when targeting Node.js v4). This work didn't properly handle export {...} declarations.

Compile the following with -t es6 -m commonjs:

export function foo() { }
function bar() { }
export { bar };

Expected output is:

function foo() { }
exports.foo = foo;
function bar() { }
exports.bar = bar;

Actual output is:

function foo() { }
exports.foo = foo;
function bar() { }

I will be putting up a fix for the problem shortly.