parameter don't use query cache"
Thanks to the fix of BUG#26842, statements prepared with SQL PREPARE
and having parameters can now use the query cache.


mysql-test/include/query_cache_sql_prepare.inc:
  now, statements prepared with SQL PREPARE use the query cache even
  when they have parameters.
mysql-test/r/query_cache_ps_no_prot.result:
  updated result: we see caching happened.
mysql-test/r/query_cache_ps_ps_prot.result:
  updated result: we see caching happened
sql/sql_prepare.cc:
  query expansion does not insert user variables' references anymore,
  it now inserts parameters' values (BUG#26842's fix did this);
  so we can use the query cache.