Do not permit find_package to cheat

Using the list of previously built packages circumvents the checking that's supposed to be done by hand by the code in this module.  We want to be absolutely sure that the installed version of Autowiring is being used, and not the one that's checked out currently.
Merge pull request #149 from leapmotion/fix-findpackagecheater

Do not permit find_package in examples to cheat