[gnome-db] API change for GdaConnection

[Vivien Malerba <vmalerba gmail com>]

Hi!

I've looked into all the providers and realized that the
"GdaParameterList *params" argument of the
gda_connection_execute_command() method is never used, so I propose to
remove it, as there is also no documentation for its usage (which is
normal considered it's never used).

This is a starting point in improving the libgda API useability.

I'm also planning to add asychronous query execution to be able to
have more responsive GUI applications. I'll submit a proposal API
before any actual implementation.

Cheers,

Vivien