Added SetNoneComparison in lang.cxx, which allows the language module to
specify how to determine whether the empty argument was given for the
'self' pointer.
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@4473 626c5289-ae23-0410-ae9c-e8d60b6d4f22