Misc. Doxygen build system improvements

- Check Doxygen version when running one of the Doxygen targets, and
  produce a note that states the expected version if there is a
  mismatch.
- Check the result of the Doxygen process and fail the build if the
  program returns an error code.
- Add a tag to all warnings that identify the type of documentation that
  produces them.  This should make it easier to understand the Jenkins
  warnings in the case not all documentation types produce a certain
  warning.

Change-Id: I030c0b2c69958fe41f0b964399cb1c2e1b250e77