Solve SSL-C breakage introduced in mod_ssl.h rev 1.129 and

  Solve SSL-C breakage introduced in mod_ssl.h rev 1.129 and
  ssl_engine_kernel.c rev 1.88.  SSL* is not const under SSL-C.

  I've confirmed Jeff's comment that the original patch doesn't harm
  earlier OpenSSL versions which declared no arguments at all.

  I suspect now that we could fold
     #define MODSSL_BIO_CB_ARG_TYPE const char
     #define MODSSL_CRYPTO_CB_ARG_TYPE const char
     #define MODSSL_INFO_CB_ARG_TYPE const SSL*
  into a single MODSSL_CB_ARG_CONST define, but this works for now.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/ssl@99263 13f79535-47bb-0310-9956-ffa450edef68