Update dir_last_modified_time function to consider both c_time and m_time for last modified time calculation
Created by: deepakduggirala
If the copy process is configured to preserve the metadata of the source file, it will set the m_time of the target file after the copy process. This will update the c_time of the target file. In these cases, c_time will be bigger than m_time. So, we will consider the maximum of c_time and m_time of the file / directory as the last modified time.