Main changes:
1. Avoid invalid writes by not passing pointers to a GArray that
realloc()s its data
2. Use a hash table to store image defs, instead of an array. This
requires a custom hash/equal function
3. Make image desc computation sync, so that setting a cs always
succeeds or always fails and doesn't depend on timing.
4. Add a few debug messages in failure paths. For lack of a category,
they ended up in MISC.
This is a still experimental protocol (thus the xx prefix).
We are using it go obtain information about the compositors
preferred color state, and pass that on to our rendering machinery.
The currently supported color states are srgb, srgb-linear, rec2100-pq
and rec2100-linear. We don't have any support for ICC profiles.
Unlike other protocols, keep the support code for this protocol
fairly isolated behind wrapper objects, since the protocol is
still subject to change.
