Issue/1692v3 OK :) I merged my fix for virtual fields. 

Hi Massimo, in an recent commit you used a different approach to detect virtual fields in the case where the fields argument is not used. I have reverted to my approach because I didn't see the advantage of your approach (or didn't understand it).

The real benefit of this PR is to fix virtual fields in the probably-more important situation where fields= is used with SQLFORM.grid