Thanks, that works!
One more question: how to add namespaces and individual classes properly? I know about the Add Reference option in the VS solution explorer context menu (but that one only accepts .dll, .exe, .manifest, etc. files) and I know that you can drag individual .cs files into the solution explorer, but I'm not sure the latter is a proper way of doing it, because I'm noticing that changes to a class from that .cs file done through a Unity-generated solution are not replicated when open that class in the server solution (suggesting that drag-and-dropping .cs files into a server solution probably creates duplicate file somewhere and not a reference). Am I missing some obvious third way of adding classes to a solution?
Let's say I want to add SimpleJSON namespace (containing just one small .cs file) into the server project in the very same way you added TNet namespace into it. How do I go about it?
Update: A-ha, looks like I was moving stuff into the solution explorer incorrectly. Instead of using root folder and dragging individual .cs file I wanted, I should have dragged whole Plugins folder into Assets folder already present in the server solution explorer, and then use "Exclude from project" context option to drop every single file but SimpleJSON.cs.