git-svn: honor ~/.subversion/ client cert file settings.

Currently, whenever svn repository http server requests client
certificate, prompt provider is invoked, ignoring any
ssl-client-cert-file settings in ~/.subversion/servers.

Moreover, it happens more than once per session, which is quite
irritating.

Signed-off-by: Michael Krelin <hacker@klever.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -2925,6 +2925,7 @@ sub new {
 	    SVN::Client::get_ssl_server_trust_file_provider(),
 	    SVN::Client::get_simple_prompt_provider(
 	      \&Git::SVN::Prompt::simple, 2),
+	    SVN::Client::get_ssl_client_cert_file_provider(),
 	    SVN::Client::get_ssl_client_cert_prompt_provider(
 	      \&Git::SVN::Prompt::ssl_client_cert, 2),
 	    SVN::Client::get_ssl_client_cert_pw_prompt_provider(