parametric nodes (or predef iterators) are nested.

Before, nested iterators were handles as follows : a source-level
(i.e., not compiled) alias node was created on-the-fly, and then
compiled. But this way to proceed was buggy for static args coming
from nested iterators or nested parametric nodes.

Now, I rely on Inline.iterators to get rid of iterators (the iterator
inlining is now recursive).