test push/pull of pandas TimeSeries
use `type(obj) is cls` as switch when canning

`isinstance(obj, cos)` would trigger the canning shortcuts for subclasses,
which can be inappropriate (e.g. pandas.TimeSeries).

closes #2793
add istype to canning

allows strict type checking, but accept tuples to check like isinstance.
Merge pull request #2800 from minrk/typecheck

use `type(obj) is cls` as switch when canning

`isinstance(obj, cos)` would trigger the canning shortcuts for subclasses,
which can be inappropriate (e.g. pandas.TimeSeries).

closes #2793