Properly follow function signature using a temporary gsize variable address
to make the function use the same pointer type and avoid troubles at
deferencing it, while use automatic-casting to switch to signed one if
transfer succeeded.
When a transfer is completed, we automatically unref it since we can't
consider it valid anymore since this point.
Update the drivers not to free the transfer after submitting anymore.
This is a rewrite of the core based on GObject and Gio. This commit
breaks the build in a lot of ways, but basic functionality will start
working again with the next commits.
