Fix the import handling in "complex" cases. When looking a.b.c and 'a' is a

module, we should look for 'b' *just* in the module 'a' and then continue
resolving b.c in the environment created by updating *with* a.

Still not 100% correct, but getting there.

src/test/compile-fail/import4.rs

@@ -0,0 +1,8 @@
+// error-pattern: recursive import
+
+import zed.bar;
+import bar.zed;
+
+fn main(vec[str] args) {
+  log "loop";
+}