LP#1070466: Print to STDERR in Sip/Checksum::debug_split_print.

debug_split_print was printing to STDOUT, which goes to the client. This
causes the client to hang up because it is not receiving the expected
response from the server.  Explicitly printing to STDERR in this
function resolves this and you can continue your session while also
debugging checksum calculations.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
LP#1070466: Pack, then unpack total in debug_split_print.

The checksum needs to be a 16bit value, so we pack, then unpack the
checksum total in debug_split_print to guarantee that.  Some longer
messages have generated 32-bit checksums.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>