/sqlite3cc

- add columns() to row that returns a boost::tuple of various types so multple

	columns can be fetched at once (look in to using BOOST_PP_ITERATE macro)

- make basic_statement and database keep a shared pointer to the database handle

	so the classes can be made copyable. The wrappers around the handle

	(implemented in sqlite::detail) can clean them up after use. This will also

	make the implementation of rows (to get round the forced non-dependency of

	rows on querys) a little easier to swallow.

	- A similar wrapper should be created for statement handles, making

		basic_statements, querys and commands copyable. Could weak_ptrs to these

		also be used in the database's list active querys?

- fix to force the finalisation of queries in progress for transactions causes

	errors; queries are now finalised twice, the second from basic_statement's

	dtor, which causes a segfault. We could:

	- keep a list of force-finalised sqlite3_stmt pointers in the database which

		we use to check queries against before finalising them to make sure we

		don't finalise them a second time

		- an efficient implementation, but not very OO

	- keep a map of active queries in the database (using the sqlite3_stmt

		pointer as the key), so that we can obtain the query and tell it to

		finalise its self

		- this seems like a messy and complicated implementation

- turn on extended errcodes in open() and handle them in sqlite_error

- use sqlite3_db_mutex() to provide extended error information during

	sqlite_error construction. The genreeal procedure would be to lock the db

	mutex, perform some sqlite3 command, check the error code, throw an

	sqlite_error (whilst obtaining extended error info) and then unlock the db

	mutex. Two options:

	- a macro would be simple

	- a templated safe-calling object (passing the comman's arg types as

		template params) may be overkill

- expand sqlite_error - perhaps use boost::system_error (see

	boost/asio/error.hpp for an example of extending system_error)

- see if we can #include "sqlite.h" in to a namespace.

	Pros:

		we better encapsulate the library

		we can reuse "sqlite3" as a namespace

	Cons:

		makes access to real sqlite stuff awkward to sqlite3cc users, but does

			this matter? they can't access database._handle anyway!

		potential incompatibility when linking to libraries that also link

			against sqlite

- query::prepare() isn't being called during construction (form

	basic_statement's constructor)