Analysis should report error when there are multiple declarations

I just spent some time wondering why my type declarations don't work.

I had

`Decl foo(X, Y, Z) descr [ extensional() ] bound [/x, /y, /z].`

and elsewhere (in a separate file) simply

`Decl foo(X, Y, Z) descr [ extensional() ].`

In my case the last one won and I couldn't get type inference to pick up the column types from `foo`.

The expected behavior is to signal an error when there is more than one type declaration in a program.