Use synchronous Gnome kering API as it results in much shorter
code and pushes the event loop handling into the Gnome library.
This may resolve the threading issues in issue 3498.

* subversion/libsvn_auth_gnome_keyring/gnome_keyring.c
  (struct gnome_keyring_baton): Remove.
  (callback_destroy_data_keyring, callback_done,
   callback_get_info_keyring, callback_default_keyring): Remove.
  (get_default_keyring_name, check_keyring_is_locked,
   unlock_gnome_keyring): Use synchronous API.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1640730 13f79535-47bb-0310-9956-ffa450edef68