elementNROWS() is generally incorrect for vector extensions

[lawremi]

The elementNROWS,ANY() calls the C-level sapply_NROWS(), relying on an error condition to fallback to the safe vapply(., NROWS, ...) path. Unfortunately, sapply_NROWS() will succeed (with a generally incorrect result) for any "object" that is implemented by a vector, including lists (very common). We could dispatch to NROWS() in that case, but it the simplest fix would be to fail whenever IS_OBJECT() is TRUE.

Like

	if (!IS_VECTOR(x) || IS_OBJECT(x))
 		error("get_NROW() defined only on a vector (or NULL)");