The logic to handle short reads/writes was incorrect, causing the
packet handler to attempt to handle incomplete packets.
Grow the packet transmit buffer in proportion to observed usage,
causing fewer reallocs.
Add some more debug in the registry chunks code.
This avoids:
* triple-checking for the GType when type-checking is enabled (see #597260)
* Avoids going through an expensive no-argument checking which landed in
glib-2.22
* Avoids going through 2 extrac functions (g_object_new -> g_object_new_valist)
Fix an off-by-one error in the size guard for unpack_element, and
improve various debug statements in the failure paths.
Also, swap some g_new0 to g_malloc0 for the fun of it.
