faint-source parallaxes

Lang and I began the process of clean rooming my IDL (yuck) code for measuring the proper motions of very faint sources in multi-epoch imaging to Python. We used a technique pioneered by Mierle and me: Connect by skype (tm) and talk while both manipulating the same emacs window via old-school unix screen (which can be attached by multiple parties simultaneously). This is very effective for communicating about the code and allowing each parties to type while the other watches even when the parties are geographically separated. We didn't finish the clean-room, but we made more progress than is common in a typical 7 person-hours, with two of us working for 3.5 hours. As my loyal reader knows, pair coding is a corner stone of the extreme programming model (which is badly named but very effective).

The reason for the clean-room is mainly to be fully open-source, but also to take advantage of the scientific equipment available in Python libraries; in particular, my dumb IDL implementation is not going to scale as we (a) add parallax estimation, and (b) run on millions of sources.