Added stringappend_test back into the unit tests.

Summary:
With the Makefile now updated to correctly update all .o files, this
should fix the issues recompiling stringappend_test. This should also fix the
"segmentation-fault" that we were getting earlier. Now, stringappend_test should
be clean, and I have added it back to the unit-tests. Also made some minor updates
to the tests themselves.

Test Plan:
1. make clean; make stringappend_test -j 32	(will test it by itself)
2. make clean; make all check -j 32		(to run all unit tests)
3. make clean; make release			(test in release mode)
4. valgrind ./stringappend_test 		(valgrind tests)

Reviewers: haobo, jpaton, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D11505

Makefile

@@ -63,7 +63,8 @@ TESTS = \
 	filelock_test \
 	merge_test \
 	redis_test \
-	manual_compaction_test
+	manual_compaction_test \
+	stringappend_test
 
 TOOLS = \
         sst_dump \

utilities/merge_operators/string_append/stringappend_test.cc

@@ -329,6 +329,26 @@ TEST(StringAppendOperatorTest,PersistentVariousKeys) {
     slists.Append("b","l;");
     slists.Append("c","rogosh");
 
+    // The previous changes should be on disk (L0)
+    // The most recent changes should be in memory (MemTable)
+    // Hence, this will test both Get() paths.
+    std::string a,b,c;
+    slists.Get("a",&a);
+    slists.Get("b",&b);
+    slists.Get("c",&c);
+
+    ASSERT_EQ(a,"x\nt\nr\nsa\ngh\njk");
+    ASSERT_EQ(b,"y\n2\ndf\nl;");
+    ASSERT_EQ(c,"asdasd\nasdasd\nbbnagnagsx\nrogosh");
+  }
+
+  // Reopen the database (the previous changes should persist / be remembered)
+  {
+    StringAppendOperator append_op('\n');
+    auto db = OpenDb(&append_op);
+    StringLists slists(db);
+
+    // All changes should be on disk. This will test VersionSet Get()
     std::string a,b,c;
     slists.Get("a",&a);
     slists.Get("b",&b);