move infer into typeck module

Author: nikomatsakis

src/rustc/middle/infer.rs renamed to src/rustc/middle/typeck/infer.rs

@@ -49,10 +49,10 @@ mod middle {
         mod reachable;
     }
     mod ty;
-    mod infer;
     mod ast_map;
     mod resolve;
     mod typeck {
+        mod infer;
         mod astconv;
         mod collect;
         mod vtable;