ActiveRecord SQLite adapter: extralite instead of sqlite3

[dbackeus]

With this diff all the sqlite3_adapter tests pass: 70 runs, 120 assertions, 0 failures, 0 errors, 0 skips

TODO

• Remove strict option (or implement support for it in the extralite gem)
• Remove the encoding option (or implement support for non UTF-8 encodings in the extralite gem)
• Remove left over dependencies on the sqlite3 gem
• Check if any other rails tests fail (I've only been running the sqlite3_adapter tests in isolation)
• Verify support for statement timeouts (I don't think I have this covered automagically, but since tests are passing it's hard to say)

Questions

• Does it matter that extralite uses symbols instead of strings for column names?
• Does it matter that execute returns Integer instead of Array result set?