Simplify the ssl_asn1_table API, remove abstraction (it is used only

Simplify the ssl_asn1_table API, remove abstraction (it is used only
to cache serialized EVP_PKEYs not any char * blobs), and document.

* modules/ssl/ssl_util.c (ssl_asn1_table_set): Take the EVP_PKEY and
  serialize internally.  Use ap_realloc.  Return the ssl_asn1_t *
  pointer.  Don't call apr_hash_set() for unchanged pointer case.

* modules/ssl/ssl_engine_pphrase.c (ssl_load_encrypted_pkey):
  Adjust for the above.

* modules/ssl/ssl_private.h: Adjust as above, add docs.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1830927 13f79535-47bb-0310-9956-ffa450edef68