tigefa4u projects Trac

The wiki engine "state" is now cached entirely in the `WikiSystem` component,
thereby associating it to the proper environment.

This was the original solution for #1750, as implemented in InterTrac.

Fixes #2138.

Inform the user that a `trac-admin ... resync` is needed
if the ''repository_dir'' has been changed since the last resync.

This adds a 'name' property to the `Repository` class (given to the constructor).
This name is ''not'' necessarily the content of `repository_dir`.
E.g. for Subversion, it's
{{{
svn:<the UUID of the repository>:<repository_path>
}}}

Closes #2107.

Improved support for SVN sub-repositories:
* the `get_path_history` is now sub-repository aware.
A few refactorings has been done to clarify the code:
* backported the `Repository.has_node(path,rev)` method from TracDiff
* introduced a `_scoped_path(scope, fullpath)` function which
truncates the scope from a full repository path, as returned by the svn API
* simplified the `_normalize_path` function
* added a bunch of unit-tests to cover the `versioncontrol` API
in the sub-repository case
* fix `log:@123:234` links (i.e. if no path is given, take the root)

This fixes #1930.

Small fixes for attachments:
* Attachment unit tests could fail when the timestamps are identical.
Fix contributed by David James.
* Fixed a typo in attachment.py spotted by lelit.

TracDiff: choose a better name for the method providing the summary of arbitrary changes (`s/Repository.get_deltas/Repository.get_changes/`). Suggested by lelit on IRC.

InterTrac: merged in changes from TracDiff (log:branches/cboos-dev/anydiff-branch@...:2306)

InterTrac: updated built-in Wiki documentation

TracDiff: added an informative title for `diff:` TracLinks and did some refactoring

display a warning in tracd if the project paths conflict (fixes #2124)

TracDiff: adapted wiki TracLinks syntax for `diff:` to use "@" as a path/revision separator