R1:e15da7568734

Generated code> make it harder to mark code as generated

Summary: It's now harder to accidentally mark code as generated.
Test Plan:
Tested with this diff in my sandbox; only file "D" was shown, the others
were marked as generated:

diff --git a/A b/A
index e69de29..780b46c 100644
--- a/A
+++ b/A
@@ -0,0 +1,2 @@
+@generated
+Tue Jun 7 16:41:17 PDT 2011
diff --git a/B b/B
index e69de29..b55fe21 100644
--- a/B
+++ b/B
@@ -0,0 +1,3 @@
+/**
+ * @generated by ed
+ */
diff --git…