[R-Forge #5661] setDT should check if binding is locked before to assign

[arunsrinivasan]

Submitted by: Arun ; Assigned to: Nobody; R-Forge link

As posted here on SO.

To check probably: bindingIsLocked(., env_where_it_resides) should return FALSE before to assign?

[arunsrinivasan]

Closing this now with an error in case setDT is attempted on a variable whose binding is locked. But tagging @mattdowle so that we can discuss changes if necessary.

Also update the SO post with an answer.