src: close libuv handles on exit

Commit 556b890 added a call to uv_loop_delete() with the intent of
catching handle lifecycle bugs.  It worked because it exposed one:

    process.on('exit', function() {
      console.log('bye');  // Asserts.
    });

When run, it asserts with the following message:

    Assertion failed: (!uv__has_active_reqs(loop)), function
    uv__loop_delete, file ../deps/uv/src/unix/loop.c, line 150.

That's because libuv as of joyent/libuv@3f2d4d5 checks that there are
no in-flight requests when the event loop is destroyed.  In the test
case above, the write request for the string hasn't completed yet by
the time node.js exits: the string itself has most likely been written
but libuv hasn't had the opportunity to return the write request to
node.js.

That's why this commit adds a cleanup step right before exit where it
explicitly closes all open handles, then waits until the event loop
exits naturally.

Named pipes (UNIX domain sockets) are shut down first in order to flush
pending write requests.  Should go some way towards fixing the Windows
issue where output on stdout/stderr sometimes gets truncated.

Fixes joyent/libuv#911.
test: move smalloc segfault tests to pummel

These tests take a while to complete, and the issue only potentially
appears under heavy load.
Revert "src: close libuv handles on exit"

This change is not entirely ready for prime time: it's making ~50 tests
fail on Windows, mostly due to timeouts.  It's up for debate who is
at fault here: node.js or libuv.

It does however expose a libuv bug on OS X, where the event loop
sometimes gets stuck in uv__io_poll() when there is a single
UV_SHUTDOWN request left in the queue.  Needs further investigation.

This reverts commit 4915884da69814bd4daab22393919a628c9ecf23.
Revert "src: call uv_loop_delete() on exit in debug mode"

Don't call uv_loop_delete() until we've figured out a way to gracefully
close open handles.  See also commit 4915884 and its subsequent revert
in commit 980cbd5.

This reverts commit 556b890ad91780c52c77dccaddcf69beb8184e27.