Improvements to mempool reference auditing feature

Improvements to mempool reference auditing feature

- New audit-point macro for atomic writes
- Check imageset list directly (instead of indirectly through image
  list)
- Check dynamic images and have special rules for them (for the time
  being we will allow dynamic images to point to non-dynamic ones
  without auditing, long-term this is a FIXME)
- Print image names out with more detail (image sets get full names)
- Remove some #if CHECKED_BUILDs
- New g_assert_checked asserts for checked builds only