tigefa4u projects Trac

Ported [2901] and [2902] to 0.9-stable (fixing #2006 and #2544).

Two attempts to fix #2006:
* based on patch by Markus Fuchs, flush the CGI standard output stream after headers have been written.
* fix the `http_date` format to pad the day with a zero for 2 digits.

Fix for #2544 (focus style for all ''textwidget''s).

VcRefactoring: reintroduce non-greedy match for InterTrac prefix in shorthand links.

This fixes the change made in [2872], when support for hex digits in changesets was added. Note that I got the comment wrong there, as that changeset actually made the match ''greedy''.

The problem with greediness is that changesets starting with hex digits can't be recognized at all (e.g. in `[b47]`, "b" will be the intertrac prefix).

Therefore, I think it's better to drop support for links like `[trac2781]` that motivated the original change, as there are alternatives: either `[trac 2781]` or `[T2781]` if "T" is set as an alias for "trac".

VcRefactoring: make use of the `short_rev` form of a revision number in the old/new revision columns of the inlined TracChangeset view, where horizontal space is limited.

TracMercurial: some internal rename and cleanup

VcRefactoring: VC plugins should use the `trac.versioncontrol` namespace.

More specifically, a backend providing the support for the `repository_type` "`xyz`" should be implemented in the `trac.versioncontrol.xyz` package.

The TracAdmin `initenv` command can automatically enable the appropriate plugin, and the initial repository `sync` can even succeed if the corresponding plugin has been installed globally.

See also TracDev:195

Ported [2895] to 0.9-stable (fixing #2330).

Fix for links in report rows when the columns don't include a visible ID column (#2330).

VcRefactoring: follow-up to r2889: finalize the implementation of the ''extra changeset properties'' feature.