• Add getSecurity() method to support security descriptors query via SMB2. (Contributed by @koniiiik)
• Improve retrieveFile() and retrieveFileFromOffset() methods to allow file
  retrievals over SMB2 even when the file is being locked on the server.
• Silently discards NMB SESSION_KEEPALIVE packets instead of raising warnings.
• SMB sessionID will be sent in ECHO requests to conform to SMB2 specs. (Contributed by @divad)
• Fix type errors for MD4 functions in python3. (Contributed by @viatoriche)