deprecated auto_expand_choker. started factoring out choker logic into its own translation unit (preparing for making it unit testable)

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code/trunk@10436 a83610d8-ad2a-0410-a6ab-fc0612d85776
factored out choke comparison functions into choker.cpp

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code/trunk@10437 a83610d8-ad2a-0410-a6ab-fc0612d85776