Issue #119 - Test HTML4, custom-tags: no

# About this case

This test case ensures that Tidy handles autonomous custom tags appropriately for pre-HTML5 documents. Tidy will support them via the `custom-tags` option, even though such documents do not support such tags.

In this case, `custom-tags` is no, and so Tidy should report unknown tags. We will use `force-output` to ensure that a document is generated, and to gather additional warning output.

This is a user-defined tag, and Tidy should provide a warning, but allow it. This is a user-defined tag, and Tidy should provide a warning, but allow it. Because `custom-tags` is no, it's treated like any other user-defined tag, even though it looks like an autonomous custom tag. This is an autonomous custom tag, but it's not supported in this test case. It should be rejected and cause an error.