GdaClient acts right now as a connection sharing mechanism. That is, it
keeps a list of open connections, and shares them (opening one connection
only to each database/user/password combination).

It would be really nice to have more features:
* make it work as a normal pool, allowing the opening, at startup, of a given
  set of connections, thus being available when the first client tries to
  connect.
* allow extra life of connections, allowing, in the API, the setting of
  a given timeout to specify the time that connections should be kept
  around after the last client disconnects.