enhance generated code auditing

[scotthart]

The generate-libraries build currently detects changes in existing files or adding of new files, but it doesn't account for extraneous files that should not exist.

One possible solution would to have the generate-libraries build git rm all the .h files in the directories of generated code to make sure they are replaced by running the generator. We would want to exclude any build, documentation, or streaming.cc files from being removed as the generator may not replace them exactly.