Every policy's documentation has a paragraph on what version of CMake
introduced it, how to set the policy, and whether CMake warns if the
policy is not set. The wording of this paragraph has diverged across
policies over time. Factor the paragraph out into a standard advice
document included by every policy.
This commit adds a new CMake policy, CMP0080, which prohibits the
inclusion of BundleUtilities at configure time. The old behavior is
to allow the inclusion.
Alex Turbov