xulrunners. this was necessary for smooth migration, since we want
plugins work for mozilla 1.8 branch too (seamonkey, thunderbird);
they are upwards-compatible if built against 1.8. however, some
new applications started to depend on 1.9, and also other (non-plugin)
apps will start to migrate so that the old xulrunner can go away
requested by many; bulk build & pkgpath & bump done by sthen@
