context is not always restored by parallel operations

[bjouhier]

To repro, modify the contexts test (

f-promise/test/f-promise-test.ts

Lines 149 to 150 in fab7d47

	var promises = [run(() => testContext(3)), run(() => testContext(5))];
	deepEqual(promises.map(wait), [7, 11]);

) as follow:

        isObject(context());
        var promises = [run(() => testContext(3)), run(() => testContext(5))];
        deepEqual(promises.map(wait), [7, 11]);
        isObject(context());

the second isObject test fails.