Compact blocks MSG_CMPCT_BLOCK enum value is already in use. It is used as MSG_THINBLOCK for xthin blocks.

The existing type MSG_THINBLOCK is already in use and widely deployed:
In Bitcoin XT, Bitcoin Classic and Bitcoin Unlimited.

Please consider changing the enum value to an available one. I plan to add compact blocks to XT and I'd rather not have to guess the enum values meaning from context.