Lots more debugging information:
* Debug active operations, number of
constructed/destructed/begun/completed/synchronously-completed
operations
* Remove some useless checks (inCallback, callbackPending) when in fact
callbackPending was causing callbacks to sometimes be missed
* Throw an error if free() called while an operation is active (rather
than eventually assert()ing)
* Correctly null out EosHandle::hWait_ when FreeHandle() called
* Rename and simplify IOperation/Operation
Fix the async keep-alive issue

Done by creating new async handles each time. The problem that was
async_close doesn't really close the handle until the next tick, however
before that point we might have already created a new handle,
overwriting the one which is about to be closed!

* Also revert back to having the bindings as the default export
* Add a function in debug mode to return active handles (i.e. those
which have a positive reference count)
* Fix some node 0.10 compile errors
*