tigefa4u projects Trac

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

Follow-up to r2268: I actually had some more unit tests about the features fixed and added

A few enhancements and bug fixes for labelled TracLinks:
* don't strip the namespace of external links if no label is given (fixes #2029)
* labels can be quoted with '...' or "..." (identical to the way the target can be quoted)
* both target and label can be omitted (links like `[search:]` are possible)