[yt-dev] Issue #627: field_list on geometry needs to have the field types as well as field names (yt_analysis/yt)

[Matthew Turk]

New issue 627: field_list on geometry needs to have the field types as well as field names
https://bitbucket.org/yt_analysis/yt/issue/627/field_list-on-geometry-needs-to-have-the

Matthew Turk:

Currently, much of the field detection code is complicated by the fact that we have fields like `"Density"` inside the `field_list` as opposed to `("gas", "Density")`.  We should resolve with two improvements:

 * `field_list` should be a subclass that checks against the various items and field types
 * `field_list` should also only have the proper tuples

Once this has been done, much of the code in the field detection and dependency verification can be eliminated.

Responsible: MatthewTurk