client.c: Added update option

The client now checks if it was called with update option. If that is true,
the client will check for updates and finalize execution, returning
appropriate messages. Otherwise, the client will not check for updates, but
will send the availability data to the server.

Signed-off-by: ERIK ALEXANDRE PUCCI <eap08@c3sl.ufpr.br>
Acked-by: Bruno Ribas <ribas@c3sl.ufpr.br>
Acked-by: Diego Giovane Pasqualin <dgp06@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>