Update smbserver.py and negtelnetserver.py to be compatible with
Python 3 while staying backwards-compatible to support Python 2.
Fix string encoding and handling of echoed and transferred data.
Tested with both Python 2.7.17 and Python 3.7.7
Reported-by: Daniel Stenberg
Assisted-by: Kamil Dudka
Reviewed-by: Marcel Raad
Fixes#5104Closes#5110
Users of the SMB tests will have to install impacket manually.
Reasoning: our in-tree version of impacket was quite outdated
and only compatible with Python 2 which is already end-of-life.
Upgrading to Python 3 and a compatible impacket version would
require to import additional Python-only and CPython-extension
dependencies. This would have hindered portability enormously.
Closes#5094
When extracting a <section> <part> and there's no </part> before
</section>, this now outputs an error and returns a wrong string to
make users spot the mistake.
Ref: #5070Closes#5071
