Add SWIG/Python support for svn_fs_freeze().

* subversion/bindings/swig/include/svn_types.swg
  Add typemap for svn_fs_freeze_func_t (Python only).

* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.h
  (svn_swig_py_fs_freeze_func): New function.

* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.c
  (freeze_func): Was svn_swig_py_repos_freeze_func().
  (svn_swig_py_repos_freeze_func, svn_swig_py_fs_freeze_func): Now/new
    wrapper around freeze_func().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1468566 13f79535-47bb-0310-9956-ffa450edef68