Node 0.8 support

[timoxley]

TODO something like:

var stream = require('stream');
// Node 0.8.x support
if (!stream.Readable || !stream.Transform) stream = require('readable-stream');

[timoxley]

depends on adding 0.8 support to stream-stream and 0.8 support for stream-sink, the former depends on stream-stream tests passing :D

[Floby]

0.8 for stream-sink is trivial and only needed for tests.
0.8 for stream-stream is different...