[R-Forge #5321] attempt to create POSIXlt columns should cause error / warning

[arunsrinivasan]

Submitted by: brodie gaslam; Assigned to: Arun ; R-Forge link

Right now, it's perfectly possible to create POSIXlt columns in data tables, leading to understandable confusion when bizarre behavior ensues. To the extent this is not supported, constructors for data table should throw errors or warning. References:

http://stackoverflow.com/questions/21487614/error-creating-r-data-table-with-date-time-posixlt

Also, another one that I can't find now where there were weird errors when attempting to head or print a data table with such columns.