Add support for cleaning up externals via 'svn cleanup --include-externals'.This should address the feature request from issue #2325.* subversion/include/svn_client.h (svn_client_cleanup2): Add include_externals parameter.* subversion/include/svn_wc.h (svn_wc_notify_t): New action svn_wc_notify_cleanup_external.* subversion/libsvn_client/cleanup.c (remove_unversioned_items_baton): Rename to ... (cleanup_status_walk_baton): ... this, and replace notify/cancel support members with a client context member which includes them. (do_cleanup): New helper function, extracted from svn_client_cleanup2(). (remove_unversioned_items): Rename to ... (cleanup_status_walk): ... this, and extend to optionally clean up externals found during the status walk. Adjust for baton changes, too. (svn_client_cleanup2): New parameter include_externals. Call the do_cleanup() helper function which replaces most of this function's body.* subversion/libsvn_client/deprecated.c (svn_client_cleanup): Account for new parameter to svn_client_cleanup2().* subversion/svn/cleanup-cmd.c (svn_cl__cleanup): Pass opt_state->include_externals to svn_client_cleanup2().* subversion/svn/notify.c (notify): Handle svn_wc_notify_cleanup_external.* subversion/svn/svn.c (svn_cl__cmd_table): Add --include-extenals option to 'svn cleanup'.* subversion/tests/cmdline/wc_tests.py (cleanup_dir_external, test_list): New rather simple test.