Add a test that imports can't circumvent exports

Author: brson

src/test/compile-fail/export-import.rs

@@ -0,0 +1,19 @@
+// xfail-boot
+// error-pattern: unresolved name
+
+import m.unexported;
+
+mod m {
+  export exported;
+
+  fn exported() {
+  }
+
+  fn unexported() {
+  }
+}
+
+
+fn main() {
+  unexported();
+}