Separate payload archive close and free
- When writing, archive finalization can write further data into
the payload (eg cpio trailer). We need to be able to fish the
final archive size *after* closing it, otherwise archive size
will be off by trailer size.
- Add new rpmcpioFree() function which simpy frees the archive struct,
calling rpmcpioClose() in the process if it wasn't already done.
- This also simplifies the error code gymnastics in fsm: we need to
free the resources whether error or not, which rpmcpioFree() allows
us to do. And for writers, calling rpmcpioClose() only needs to
be done if earlier parts were successfull, so we dont need to worry
about masking a former error code when calling it.