Use the new uv_ref()/uv_unref() API for node >= v0.7.9, and remove a couple
unnecessary instances of uv_ref()/uv_unref() where only uv_queue_work() was
being used.

Conflicts:
	package.json

This reverts commit f82a33f7.

This reverts commit 2b911758.

So that npm doesn't try to automatically compile and use it on an
`npm install` of the tarball.

Conflicts:
	wscript

Conflicts:

	src/database.cc

No idea really if this helps anything...

This is how node does it so let's stay consistent.