Introduce a number of SSLC hints to mod_ssl, including the following

  Introduce a number of SSLC hints to mod_ssl, including the following
  type overrides;

    MODSSL_CLIENT_CERT_CB_ARG_TYPE
    MODSSL_PCHAR_CAST      (for a host of non-void/const sslc values)
    modssl_read_bio_cb_fn  (for several callbacks with same prototypes)

  Declare callback functions appropriately.

  And protect us from indetermineant toolkits with
  #error "Unrecognized SSL Toolkit!"

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99183 13f79535-47bb-0310-9956-ffa450edef68