mozilla-i18n.sh: Fix initialisation of _F_xpi_installpath and _F_xpi_product (avoid bug in xpi.sh that creates a dummy '-extensions' group).
firefox-i18n-31.0-2-x86_64

* Rebuild against last mozilla-i18n.sh changes.
thunderbird-i18n-31.0-2-x86_64

* Rebuild against last mozilla-i18n.sh changes.