Basic auth for Solr output connector not working for POST/DELETE requests

From https://github.com/apache/manifoldcf/pull/113

The underlying Apache HTTP client uses universal basic auth for the first request, then caches the resp. auth-related data and switches to pre-emptive basic auth for subsequent requests that target the same host. This seems to cause problems requests that alter state at Solr (POST/DELETE). This situation can be easily remedied by enforcing pre-emptive basic auth for the first request.