Add SWIG python support for svn_repos_freeze.

* subversion/include/svn_repos.h
  (typedef svn_repos_freeze_func_t): New.
  (svn_repos_freeze): Use typedef.

* subversion/libsvn_repos/repos.c
  (struct freeze_baton_t, svn_repos_freeze): Use typedef.

* subversion/svnadmin/svnadmin.c
  (freeze_body): Add comment.
  
* subversion/bindings/swig/include/svn_types.swg
  (svn_repos_freeze_func_t): New.

* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.h
* subversion/bindings/swig/python/libsvn_swig_py/swigutil_py.c
  (svn_swig_py_repos_freeze_func): New.

* subversion/bindings/swig/python/tests/repository.py
  (setUp): Store repository path.
  (freeze_body): New callback.
  (test_freeze): New test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1464939 13f79535-47bb-0310-9956-ffa450edef68