Swap out q-io for needle on server-side jQuery.ajax shim

Here's my first PR. I didn't rebuild the dist files or anything like that yet -- I'm going to submit another patch or two and wanted this to merge cleanly. @duerig, let me know what you think.

My plan is to enable multipart uploads (and non-json POST
bodies) with needle. This should also support HTTP compression,
and fix the server-side API.