Add some tests of tag-export interaction

src/test/compile-fail/export-no-tag-variants.rs

@@ -0,0 +1,17 @@
+// xfail-boot
+// error-pattern: unresolved name
+
+// Tag variants are not exported with their tags. This allows for a
+// simple sort of ADT.
+
+mod foo {
+  export t;
+
+  tag t {
+    t1;
+  }
+}
+
+fn main() {
+  auto x = foo.t1;
+}

src/test/run-pass/export-abstract-tag.rs

@@ -0,0 +1,19 @@
+// We can export tags without exporting the variants to create a simple
+// sort of ADT.
+
+mod foo {
+  export t;
+  export f;
+
+  tag t {
+    t1;
+  }
+
+  fn f() -> t {
+    ret t1;
+  }
+}
+
+fn main() {
+  let foo.t v = foo.f();
+}

src/test/run-pass/export-tag-variant.rs

@@ -0,0 +1,12 @@
+// Export the tag variants, without the tag
+
+mod foo {
+  export t1;
+  tag t {
+    t1;
+  }
+}
+
+fn main() {
+  auto v = foo.t1;
+}