Something strange is happening to hash maps. I'm still investigating but
want to get my snapshot built in the meantime. (Problem only happened on
OS X.)
In particular, use the ast::method type to represent a class method,
and try to reuse as much iface code as possible. (This makes sense now
since I'll be allowing polymorphic class methods.)
Cross-crate metadata for classes works well enough that programs with
classes in other crates compile successfully, but output wrong results.
Checking in work so far to avoid merge hassles. (Tests are xfailed.)
This makes it possible to move them between crates without confusion,
and to instantiate them at a point where the monomorphizing
substitutions are known.
Issue #1944
Programs using classes with fields only (no methods) compile and run,
as long as nothing refers to a class in a different crate (todo).
Also changed the AST representation of classes to have a separate
record for constructor info (instead of inlining the fields in the
item_class node), and fixed up spans and pretty-printing for
classes.
