For a long time, there was a confusion between aliased types and named types (due to my misunderstanding of alias types in Go at that time). The type category `aliasT` has been renamed into `linkedT`, which is correct semantically.
Aliased types are only declared using `typeSpecAssign`, and its processing is now distinct from `typeSpec` statement, used for named types.
A `linkedT` type is obtained by a statement like `type A uint32`, where `A` type category is therefore `linkedT`.
An aliased type is obtained by a statement like `type A = uint32` (notice the `=` sign, translating into `typeSpecAssign`).
The semantic difference is that in the first linkedT form, `A` and `uint32` are 2 distinct types, instead of being strictly equivalent in the `typeSpecAssign` form (the 2 names lead to one type definition).
Fixes#1416.