test: test that closing a poll handle doesn't corrupt the stack

This is a regression test for an issue that was originally reported
in https://github.com/libuv/libuv/pull/36, and fixed in cd89452.

PR-URL: https://github.com/libuv/libuv/pull/48
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>