Asynchronously declared nested tests w/ plan() w/o end()

[andrewdeandrade]

Since substack/tape shares many of the same tests with isaacs/node-tap (I assume the tests here came from node-tap), I am adding a test from node-tap that I wrote to tape.

Recently I added (to node-tap) support for asynchronously declaring nested tests to node-tap when you've given a plan() (the plan() lets it knows to wait for asynchronously created nested test harnesses). I added this same test to tape in this pull request. No further modifications were needed to tape since this test passed right out of the box. ... Plus it never hurts to have more tests. :)

Here is the PR on node-tap from where this test was pulled from: tapjs/tapjs#103