Fix SharedPrefsBackupHelper so it doesn't hard code the paths to the files.

This took quite a bit of refactoring.
diff --git a/include/utils/BackupHelpers.h b/include/utils/BackupHelpers.h
index 24b6c9e..1d0daa7 100644
--- a/include/utils/BackupHelpers.h
+++ b/include/utils/BackupHelpers.h
@@ -118,7 +118,7 @@
 };
 
 int back_up_files(int oldSnapshotFD, BackupDataWriter* dataStream, int newSnapshotFD,
-        char const* fileBase, char const* const* files, int fileCount);
+        char const* const* files, char const* const *keys, int fileCount);
 
 
 #define TEST_BACKUP_HELPERS 1
@@ -127,6 +127,7 @@
 int backup_helper_test_empty();
 int backup_helper_test_four();
 int backup_helper_test_files();
+int backup_helper_test_null_base();
 int backup_helper_test_data_writer();
 int backup_helper_test_data_reader();
 #endif