Fix GPL violation and prompt protection in console

Two console fixes:

1. Switch to the Editline library (BSD-licensed) instead of Readline, to avoid violating the GPL requirements of Readline. As an added bonus, this also brings console history to OSX.
2. Properly pass the prompt down to the Editline call, so that the prompt can be properly protected.

Tested as working on Linux (Ubuntu 14.04, "trusty") and OS X (10.9, "Mavericks"). Editline is bundled by default on at least OSX 10.9, and the 3 most recent LTS versions of Ubuntu (14.04, 12.04, 10.04).