Revert of 9385 (which removed GSS_TSIG functionality) and rebase to master

Revert of 9385 (which removed GSS_TSIG functionality) and rebase to master

Reformat according to project settings

We prefer C++ style casts and change NULL into nullptr

Move includes from gss_context.hh to gss_context.cc if possible, remove unused ones and move from boost::shared_ptr to std::shared_ptr.

Protect access to global maps by a mechanic translation to use
LockGuarded. The scopes of the locks should be verified, they might need
to be wider!