On the 'auth-notification' branch: Add the plumbing needed to transmit
notifications from the auth subsystem, and some code to exercise it.

* subversion/include/svn_auth.h
  (svn_auth_notify_action_t): New enum type for notification actions.
  (svn_auth_notify_func_t): New function type.
  (svn_auth_provider_t): Add 'provider_name' member to the end of this
    structure.
  (SVN_AUTH_PARAM_NOTIFY_FUNC, SVN_AUTH_PARAM_NOTIFY_BATON): New auth
    parameter names.

* subversion/include/svn_cmdline.h,
* subversion/libsvn_subr/cmdline.c
  (svn_cmdline_create_auth_baton2): New function.
  (svn_cmdline_create_auth_baton): Deprecate this one as a wrapper
    around the revised API.  ### Need to move this to deprecated.c

* subversion/libsvn_auth_gnome_keyring/gnome_keyring.c,
* subversion/libsvn_subr/simple_providers.c
  Add provider names to svn_auth_provider_t structures.

* subversion/libsvn_subr/auth.c
  (svn_auth_first_credentials, svn_auth_next_credentials,
   svn_auth_save_credentials): Look for notification function and
    baton in the auth baton parameter set, and notify about relevant
    actions.

* subversion/svn/svn.c
  (auth_notify): New implementation of the svn_auth_notify_func_t
    callback type.
  (main): New use svn_cmdline_create_auth_baton2(), passing an auth
    notification function iff the "SVN_AUTH_NOTIFY" environment variable
    is set.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/auth-notification@1484895 13f79535-47bb-0310-9956-ffa450edef68