Introduce 'svn auth', a subcommand for managing the authentication cache
which supersedes the 'svnauth' tool. Currently, cached credentials can be
listed and removed. In the future, this subcommand could also provide a
mechanism to add credentials to the cache.

* subversion/svn/auth-cmd.c: New file based on subversion/svnauth/svnauth.c.

* subversion/svn/cl.h
  (svn_cl__opt_state_t): Add 'show_passwords' option.
  (svn_cl__auth): Declare.

* subversion/svn/svn.c
  (svn_cl__longopt_t): Add 'opt_show_passwords'.
  (svn_cl__options): The --remove option is also used by 'svn auth'.
   Adjust its documentation accordingly. Add a --show-passwords option
   for use by 'svn auth'.
  (svn_cl__cmd_table): Add 'svn auth' subcommand.
  (sub_main): Handle new --show-passwords option.

* subversion/tests/cmdline/getopt_tests_data/svn--help_stdout,
  subversion/tests/cmdline/getopt_tests_data/svn_help_stdout:
   Adjust expected output.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1572105 13f79535-47bb-0310-9956-ffa450edef68