Add warning when de/serializing container of thrift structs
Add warning when de/serializing container of thrift structs

Summary: This is unsupported, and we often get bug reports when it fails or does something else unexpected. Print a warning to help self-diagnose the problem.

Reviewed By: vitaut

Differential Revision: D29853203

fbshipit-source-id: bc501df2e9fc24afb863d04b77be875454d2b639

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift