Use _v2 APIs for SQLite version 3.6.13 and above.

This PR tries addresses the issue mentioned [in the mailing list](http://kepler-platform-mailing-list.1133559.n2.nabble.com/luasql-sqlite3-fetch-from-pragma-td5589445.html) a while ago.

Some pragmas won't return a cursor anymore since SQLite 3.6.23. Using _sqlite3_open_v2_ and _sqlite3_prepare_v2_ fixes that.