Fix some failing test cases from toml-test

[arp242]

These are a few issues I found investigating failing test cases from toml-test, most are fairly simple low-handing fruit. There's still a few others that fail, but this already improves things.

Instead of sending 8 different pull requests it seemed easier to batch them in one; see the commit messages for more detailed explanations on the issues.

make check will now all run all the tests (unittest + stdex tests + toml-test), and will skip toml-test tests known to fail. Can also add GitHub action for this if you want.