I defined a new download method @SAVANNAH in include/download.mk and scripts/download.pl,
and converted quilt and qemu to use that method.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42840 3c298f89-4303-0410-b956-a3cf2f4a3e73