Some more refinement of the new editor code: - add cancellation support into the core editor - assert that callbacks are provided, if they get invoked
* subversion/include/svn_editor.h: (svn_editor_create): accept CANCEL_FUNC and CANCEL_BATON params
* subversion/libsvn_delta/editor.c: (svn_editor_t): add CANCEL_FUNC and CANCEL_BATON members (svn_editor_create): add CANCEL_FUNC and CANCEL_BATON params, and store them into the editor structure. (svn_editor_add_directory, svn_editor_add_directory_streamy, svn_editor_add_file, svn_editor_add_symlink, svn_editor_add_absent, svn_editor_set_props, svn_editor_set_text, svn_editor_set_target, svn_editor_delete, svn_editor_copy, svn_editor_move): call the new cancellation functions, and test for the callback (svn_editor_complete, svn_editor_abort): test for the callback. these functions do not test for cancellation since they are the last things to be called, and we may as well let them wrap up.