am 1a3b3d48: merge from open-source master

Merge commit '1a3b3d48413d9134738c9b457292fb2b71a5dfe4' into kraken

* commit '1a3b3d48413d9134738c9b457292fb2b71a5dfe4':
  Add some documentation about the thread safety of Cursor and some of the SQLite* classes.