The entire OpenJDK infrastructure seems to be down at present. Not to fear, you can still build IcedTea6 with the latest OpenJDK6 build drop, b17, right now:

$ hg fclone
$ hg clone
$ cd icedtea6; ./; cd ..
$ mkdir icedtea6-build
$ cd icedtea6-build
$ ../icedtea6/configure --with-openjdk-src-dir=$PWD/../jdk6
$ make

Thanks to Mark Wielaard for supplying the OpenJDK6 forest backups.

Happy hacking!