Gallium3D's Galahad, as said by the initial commit by Corbin Simpson, is "a sanity-checking layer meant to replace the crufty and scattered sanity checks inside drivers with a robust, non-silenceable, useful set of warnings and errors that can be used to keep misbehaving state trackers from going unnoticed." Galahad is mostly based upon the Gallium3D "identity" driver and will report warnings like format mismatches and operations being requested but ignored.
Over the past week this code has been worked on and now it's been hooked into the build system and has been added to the targets for the R300g and i915g Gallium3D hardware drivers.
The code to the Galahad driver can be found in this directory. This driver really shouldn't be exciting for end-users, but should be useful for Gallium3D developers and those debugging problems atop this graphics driver architecture.