Revision 1665901

Following up on r1665886, add regression test on how the prompt function
is called based on the settings in both the auth and slave auth baton.

* subversion/tests/libsvn_subr/auth-test.c
  (plaintext_baton_t): New struct.
  (plaintext_prompt_cb): New function.
  (test_save_cleartext): New function.
  (test_list): Add test_save_cleartext.