coerce provides more informative error on bad datashape
Raise informative error on disagreeable datetime

Discover and dynd disagree about certain datetime formats
Lets make sure that we raise an informative error in these cases.
use dynd raw rather than coerce.  Get more particular error.
use str(schema) rather than datashape in nd.array
py3: errors don't use .message, use .args[0]
expand csv dynd error to include TypeErrors
Merge pull request #774 from mrocklin/coerce-error-reporting

coerce provides more informative error on bad datashape