i18n: conditionally import `setup_18n` from `genshi.filters`, as this function is only present in Genshi:source:branches/experimental/advanced-i18n for now.
Trac 0.12dev therefore remains usable with Genshi 0.5.1, but the templates won't be translated.
Authored by: cboos 2008-11-24
Parent: [r7706]
Child: [r7708]
