rqlquery #17070423 Add a "currentUser" function [open]

(discussed briefly with Florent)

The idea is to be able to build rql like
"Any X, U WHERE X is_instance of xzy, X created_by U, U = currentUser()"
(in bookmarks, typically)

(pardon my poor rql)

prioritynormal
typeenhancement
done in<not specified>
closed by<not specified>