tigefa4u projects Trac

TracCrossReferences: support for !ChangesetObject and !SourceObject added

The support for !ChangesetObject has to be improved, though.
In particular, a `resync` won't update the cross-references
for the changesets.

TracCrossReferences: a !TracObject can be either "cheap" or "complete"

It's essential that !TracObjects could be created with minimal cost,
for easily accessing all the basic functionality expected from a Trac object
(`shortname()`, `href()`, `wiki_to_*()` and all the xref facilities).

But at the sub-class level, the Trac object generally needs
to be filled with some data from the db in order to be useful.

The first goal (''"cheap" Trac object'') is achieved by using
either the `TracObject.factory()` or the sub-class constructor
''without'' specifying the `id` of the object.
The `id` is specified after the fact by using `TracObject.setid()`.
By the way, the factory itself rely on that mechanism.

The second goal (''"complete" Trac object'') is achieved by
giving the `id` parameter to the sub-class constructor,
or by calling `TracObject.reload()` on a "cheap" !TracObject.

Adopt SVN-like peg revision notation, as suggested in #2011.

`source:` links can now use the "@" delimiter instead of the "#" delimiter
for targeting a specific revision.

Note that the old way is still supported for backward compatibility.

Refactored the rendering of attachements and repository files so that they share the same code. Fixes #1345.

Sort the project listing in a case-insensitive way. Fixes #2088.

Cosmetic fixes (PEP:8) for `svn_fs.py`

Fixed ''search'' and ''query'' URIs so that the ampersands they eventually contain are escaped only once. Fixes #2042.

Allow insertion of a custom prelude at the top of the new ticket form. If a file named `site_newticket.cs` exists in `projenv/templates` it'll be included between the heading and the form. Closes #2021.

[wiki:TracAdmin trac-admin] fixes:
* In non-interactive mode, `trac-admin` will now return non-zero return codes when an error occurrs. Closes #1960.
* Removed CGI-specific config specific that was printed after executing `initenv` and replaced with more general information. Closes #2080.

A small fix for r2265, regarding the fix for #2079