Support unicode _ids.

Conflicts:
	mongo_connector/compat.py
	mongo_connector/doc_managers/doc_manager_simulator.py
	mongo_connector/doc_managers/elastic_doc_manager.py
	mongo_connector/oplog_manager.py
SolrDocManager: fix _id handling
Use u function to make _id unicode in Solr DocManager.
Fix potential unhandled AutoReconnect.