Fix many syntax warnings in smb_lm

Fix many syntax warnings in smb_lm

Now compiled with the same CFLAGS as the rest of Squid.
This is tested up to gcc 3.4 standards now. Some may still
be raised by later gcc versions.

 - fixes const correctness on several functions and globals
 - fixes .h wrapping on several files
 - adds prototype definitions for all functions
 - adds several missing includes
 - adds docs for some functions to auto-doc output

TODO:
 Not all code audited, only the bits shown broken right now.
 This helper contains a large amount of nasty duplicate code
 and re-implements several encryption algoritms that should
 probably be sourced from secure places.