agent: Fix --extra-socket on Windows.
* agent/gpg-agent.c (start_connection_thread): Rename to ... (do_start_connection_thread): this. Factor nonce checking out to ... (start_connection_thread_std): this, (start_connection_thread_extra): this, (start_connection_thread_browser): and this.
Although not tested, the code did not worked on Windows becuase we
were checning the wrong nonce.
- Signed-off-by: Werner Koch <wk@gnupg.org>