Fix to work behind a http proxy.

I found that adsbibtex was timing out on the line

    conn.request('GET', url.path + '?' + url.query)

due to `httplib` not using my proxy settings.

A bit of Googling and I discovered that the same functionality is provided by `urllib2`, which features proxy auto-detection.  It now works fine for me behind a proxy, and I've checked that it still determines the correct mirror (which was the only thing using the `getRedirect` function).