Inconsistent use of 'real'

Datashape has 3 things using the word "real" in them:
- `ds.predicates.isreal`: checks if the datashape is floating point
- `ds.real`: alias for `ctype("float64")`
- `ds.typesets.real`: contains all numeric, non-complex types

This is inconsistent, and should be corrected. I'd prefer to make `ds.predicates.isreal` check for containment in `ds.typesets.real` (expanding `isreal` to return True for integers). Removing the alias may or may not be beneficial.