- Transparent binary encoding of return values from PHP callback functions.

- Add user-space callback for the authorizer function (this is potentially
  very slow, so it needs to be implemented carefully).

- Add user-space callback to handle busy databases.

- Test-suite

  o Test how robust we are when a user-space function is registered as
    a callback for a persistent connection in script A, then script B is
	called that doesn't register the callback but does make use of the
	function in an SQL query.
	--> Our test suite doesn't allow us to test persistent connections
	    at this time :/

- If building a ZTS build, -DTHREADSAFE while compiling libsqlite

- If building a non-debug build, -DNDEBUG will disable the expensive
  asserts in the inner loop. (and double performance)

vim:tw=78
