tigefa4u projects Trac

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)

If an error occured sending a "pretty" error page, and sending a plain error page results in an `IOError`, just ignore the error. Closes #1999.

Fix some typos that slipped into [2265]. Sorry.

* Fix formatting of non-ASCII dates by using the `to_utf8()` from `format_date()`. Closes #2089.
* Clean up temporary files when executing a command through `NaivePopen` fails unexpectedly. Closes #2079.
* Remove obsolete code from `trac.util`.

* Fix rendering of trailing unchanged blocks in diffs. Closes #2090.
* Fix line numbers, column labelling and chunk separators in `PatchRenderer`. Closes #1985 and #2012.

Make `hotcopy` compatible with database drivers other than PySQLite < 2. Fixes #2016.