Make the gpg-agent pinentry not ask for confirmation of password entries and
make it re-prompt if the password is incorrect.

* subversion/libsvn_subr/gpg_agent.c:
  (ATTEMPT_PARAMETER): New macro.
  (send_options, get_cache_id): New functions with code taken out of
    password_get_gpg_agent() so it can be reused.
  (password_get_gpg_agent): Use send_options() and get_cache_id(),
    retrieve the attempt from the parameters and use it to determine
    if we should set an error message that will be displayed in pinentry.
  (simple_gpg_agent_first_creds): Set an iter_baton so we can limit the
    retries, put the iter_baton in the parameters so password_get_gpg_agent()
    can access it.
  (simple_gpg_agent_next_creds): New function, removes the cached password
    and prompts the user again.
  (gpg_agent_simple_provider): Add simple_gpg_agent_next_creds callback.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1600781 13f79535-47bb-0310-9956-ffa450edef68