[nem-en] Multiple project solutions

[vc]

> Does metadata info in VS have some common data-structure? For example
> what if you wanted to mix two languages and reference Nemerle from C#
> or C# from Nemerle?

C#/VB/MC++ project will be supported only over assembly references. MS not
open in API.

> If we are talking only about Nemerle - Nemerle cooperation,

Exactly. 

> it seems
> possible to implement in compiler API - we need to populate one
> NamespaceTree with nodes from referenced projects' TypeBuilders  (by
> GetTypeBuilders method in their NamespaceTree I guess).

And we need remove external TypeBuilders if it project has been changed.

> The little problem here is that you would need to clean builders
> during recompilation not only in current project, but also in
> referencing ones.

We use on demand compilation (NamespaceTree building). If project has been
changed we reset reference on it NamespaceTree. When user touch it project
we rebuild corresponding NamespaceTree. In it's time we can reload types
from another project (If we can understand that it has been changed).