rustc: Break some of metadata's dependencies on session

src/rustc/middle/astencode.rs

@@ -681,7 +681,8 @@ impl helpers for ebml::ebml_deserializer {
 
 impl helpers for @e::encode_ctxt {
     fn ty_str_ctxt() -> @tyencode::ctxt {
-        @{ds: e::def_to_str,
+        @{diag: self.tcx.sess.diagnostic(),
+          ds: e::def_to_str,
           tcx: self.tcx,
           reachable: encoder::reachable(self, _),
           abbrevs: tyencode::ac_use_abbrevs(self.type_abbrevs)}

src/rustc/middle/trans/base.rs

@@ -4998,6 +4998,7 @@ fn crate_ctxt_to_encode_parms(cx: @crate_ctxt)
         bind astencode::encode_inlined_item(_, _, _, _, cx.maps);
 
     {
+        diag: cx.sess.diagnostic(),
         tcx: cx.tcx,
         reachable: cx.reachable,
         exp_map: cx.exp_map,

src/rustc/middle/ty.rs

@@ -200,7 +200,8 @@ enum ast_ty_to_ty_cache_entry {
 }
 
 type ctxt =
-    @{interner: hashmap<intern_key, t_box>,
+    @{diag: syntax::diagnostic::span_handler,
+      interner: hashmap<intern_key, t_box>,
       mut next_id: uint,
       sess: session::session,
       def_map: resolve::def_map,
@@ -462,7 +463,8 @@ fn mk_ctxt(s: session::session, dm: resolve::def_map, amap: ast_map::map,
         hash_type_structure(k.struct) +
             option::map_default(k.o_def_id, 0u, ast_util::hash_def_id)
     }, {|&&a, &&b| a == b});
-    @{interner: interner,
+    @{diag: s.diagnostic(),
+      interner: interner,
       mut next_id: 0u,
       sess: s,
       def_map: dm,