swig-py: prevent a segfaulting function from being called.  Also hide it from
swig-pl where it is unusable (raises a TypeError(!?) if called).

Found by: Clemens Gruber
URL: http://thread.gmane.org/gmane.comp.version-control.subversion.trac.devel/7811

* subversion/bindings/swig/include/svn_types.swg
  (svn_fs_set_warning_func): Hide from swig-py and swig-pl.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1515119 13f79535-47bb-0310-9956-ffa450edef68