pm.Data are not given model-relative names

[rpgoldman]

Random variables in PyMC3 are given names relative to their parent model, if that model has a name. This avoids name collisions between models made of replicated sub-components.

However, since pm.Data objects are not random variables, they do not get renamed, which means that when they are used in sub-models they don't get renamed, so give name collisions.

I know this is a terrible issue report, but I don't have time to work on it now, even to the extent of making a better bug report, because I'm fixing another two bugs! So my apologies, but I wanted to get this recorded so I don't forget to get back to it.