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- Add getSecurity() method to support security descriptors query via SMB2
- 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.
- Fix type errors for MD4 functions in python3.