Split the client certificate callback implementation into two functions,

one that uses OSSL_STORE and the ancient/original that reads PKCS#12 files.

* buckets/ssl_buckets.c
  (ssl_read_client_cert_uri): New, conditionally present. Reads certificates
   and private keys from a keystore, which can be a PKCS#12 file or an
   OS-specific certificat stor URI. The implementation was moved from
   ssl_need_client_cert() with minor changes.

  (ssl_need_client_cert): Delegate to ssl_read_client_cert_uri() first, then
   continue with the file-based attempt if no certificates were found.


git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1931058 13f79535-47bb-0310-9956-ffa450edef68

Author: brainy