Fix handling of extensions with types not known to OpenSSL in

Fix handling of extensions with types not known to OpenSSL in
PeerExtList(); parse the value as a string primitive, or else fail,
rather than rendering the raw DER blob as a string regardless of the
type:

* modules/ssl/ssl_engine_vars.c: (dump_extn_value): New function.
  (ssl_ext_list): Use it; tweak error message and free the OID object
  (thanks to drh for spotting this last issue way back).

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@946240 13f79535-47bb-0310-9956-ffa450edef68