add timeout callback for libtorrent metainfo retrieval
simplify RemoteTorrentHandler
fix all unit tests
Merge pull request #6 from LipuFei/fix_tftp_plusmetadata_removeswift

Fix RemoteTorrentHandler and all unit tests
SqliteCacheDb -> SqliteCacheDB to keep same capitalization than the rest of the code.
fix test_sqlitecachedb_upgrade.py