Example:
{{{
[logging]
log_format = ($(thread)d) Trac[$(basename)s:$(module)s] $(levelname)s: $(message)s
}}}
See http://docs.python.org/lib/node422.html for a full list of keywords that can be used.
Note however that `$(...)s` should be used instead of `%(...)` in order to prevent the !ConfigParser from trying to expand those keys himself. In addition to those keys, a few Trac specific ones have been added: `path`, `basename` and `project`. They are written the same way as the others for the sake of consistency.
This fixes #2844. Thanks to maz <mzizka@...> for the initial patch. Even if there's nothing left of that patch, he gave the incentive to get that done ;)
