[Azoth MuC] Fixed op== for OpenUrl test.
[Azoth MuC] Remove unused slot.
[Azoth MuC] throw ParseError on parse fail for #1772.
[Azoth MuC] Require reaching end of input for #1772.
[Azoth MuC] Handle parse errors for #1772.
[Azoth MuC] Covered erroneous cases with tests.

This finally closes #1772.