This patch marks the bitbake-layers script as executable and fixes the
instantiation of the BBCooker to match recent changes in the BitBake
libraries.
I've also added a brief header which demonstrates the intent and usage
as taken from Chris Larson's original commit message.
Note: this fix is not upstreamable, it's only required in Poky because of an
outstanding difference between BitBake master and Poky's BitBake.
Signed-off-by: Joshua Lock <josh@linux.intel.com>