Fix links to comments on changesets

[SebDieBln]

HTML-links to comments on changesets are broken, because they don't use the repository name. So they only work in a setup where a default repository is defined and it is the only one receiving comments.

2023-08-27 18:24:48,193 Trac[main] WARNING: [172.17.0.1] HTTPInternalServerError:
500 Trac Error (No repository specified and no default repository configured.),
<RequestWithSession "GET '/changeset/1dd1c23fc747af84d63d634d61f3eebd3c9cdb84?codecomment=3'">,
referrer 'http://127.0.0.1:30443/changeset/1dd1c23fc747af84d63d634d61f3eebd3c9cdb84/SomeRepo'

(Note the repository name SomeRepo in the referrer but it is missing in the request.)

This PR modifies the generation of hyperlinks in a way that the link always contains the repository name.

The mentioned links can be found in the list of code-comments and on top of each comment itself.