`conn_cmfe` expression should take into account time steps across databases

[JustinPrivitera]

Right now (3.4.1), conn_cmfe can give you a variable from another database, but only for the first time step. There isn't a way to have the variable you pull from another database move through time as you move the time slider for your database. If you want a particular time step, you need to ask for only that time step, meaning you have a new expression for every time step. It would be helpful if you could step through time in both databases.