AU: tolerate files that are symlinks in src image, yet not in new image.

This fixes a bug in delta diff generation.

BUG=chromium-os:12090
TEST=unittests; generated delta w/ problematic images

Change-Id: Ic48b012d0d9e4f37edbdcf4140d0fe9c4879e7cd

Review URL: http://codereview.chromium.org/6528006
diff --git a/test_utils.cc b/test_utils.cc
index 9d1b5d0..3815d7b 100644
--- a/test_utils.cc
+++ b/test_utils.cc
@@ -208,6 +208,9 @@
   EXPECT_EQ(0, System(StringPrintf("ln -s /some/target %s/sym", kMountPath)));
   EXPECT_EQ(0, System(StringPrintf("ln %s/some_dir/test %s/testlink",
                                    kMountPath, kMountPath)));
+  EXPECT_EQ(0, System(StringPrintf("echo T > %s/srchardlink0", kMountPath)));
+  EXPECT_EQ(0, System(StringPrintf("ln %s/srchardlink0 %s/srchardlink1",
+                                   kMountPath, kMountPath)));
   EXPECT_EQ(0, System(StringPrintf("umount -d %s", kMountPath)));
 
   if (out_paths) {
@@ -223,6 +226,8 @@
     out_paths->push_back("/cdev");
     out_paths->push_back("/testlink");
     out_paths->push_back("/sym");
+    out_paths->push_back("/srchardlink0");
+    out_paths->push_back("/srchardlink1");
     out_paths->push_back("/lost+found");
   }
 }