Verify db round-trip in test suite
Don't forcefully symbolize hash keys

Keys with the ":" prefix are symbolized already, and there may be keys (like
filenames) which it doesn't make sense to symbolize.
Make @meta[:files] a hash again.

This is more convenient, and we no longer run into weird symbol/string issues
now that we aren't forcing all hash-keys to symbols when loading the JSON.

Also more strictly validate the DB in some tests.
Improve DB validation in tests