tigefa4u projects Trac

Finish to make unit tests more robust in case there's a global trac.ini.

Actually, there were a lot less remaining cases than I initially thought,
as lots of `from trac.config import Configuration` lines were useless.

Closes #3700.

Made unit tests more robust in case there's a global trac.ini file around.
- all the tests that are getting their config settings from `trac.test.EnvironmentStub` are now insulated from the global trac.ini.
- the `trac.tests.config` tests are also insulated
- ... but there are remaining uses of Configuration in other tests that have not yet been insulated from the presence of a global trac.ini

Related to #3700.

IRequestFilter fixes:
- update documentation to make clear that only `post_process_request`
should be used to modify the `req.hdf`
- always try to apply filters on the way out, even in case an error
is detected and rendered.

Should fix #3655.

TracBrowser: reworked the get_path_links helper function. Fixes #3708.

Fixed WikiPageName anchors so that they can contain "." characters, but also stop at the last ".". Closes #3635.

Don't require a navigation ''category''_order property to be defined in the Chrome component, so that other categories besides ''metanav'' and ''mainnav'' can be supported. Fixes #3692.

MySQL doesn't support `CAST(x as int)` it should be `CAST(x as signed)` (fixes #3675)

Markup branch: a few clean-ups, follow-up to [3713:3714]

Markup branch: migration of the Wiki module, done the ''diff'' mode.

Markup branch: refactoring of the Changeset view template, so that the rendering of a list of diffs can be more easily reused.

- new `changeset_navigation` macro
- new `diff_options_fields` macro
- `diff_display` macro has been inlined in diff_div.html
- `diff_line_class` macro is now the `first_last` helper function