Make sure host is lowercase even when IDNA does not apply. Ban code points that could cause re-parsing problems or were banned in browsers already.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24187
https://www.w3.org/Bugs/Public/show_bug.cgi?id=24191
https://www.w3.org/Bugs/Public/show_bug.cgi?id=24257