rustc: Add a test case for previous commit

Author: pcwalton

src/test/run-pass/simple-alt-generic-tag.rs

@@ -0,0 +1,11 @@
+tag opt[T] {
+    none;
+}
+
+fn main() {
+    auto x = none[int];
+    alt (x) {
+        case (none[int]) { log "hello world"; }
+    }
+}
+