From Gerri:

Move more auth related code out of libCore into the libRootAuth plugin.
1. moves rsa*.h/.c from clib to auth (as C++ files)
2. uses the real plugin manager in TSocket::Authenticate
   (instead of the "home-made" one TSocket::LoadAuth)
3. Add a protection on fSocket in TSlave::Close


git-svn-id: http://root.cern.ch/svn/root/trunk@12418 27541ba8-7e3a-0410-8455-c3a389f83636