Download packages from github in tar.gz format instead git format.

Verified way how to get packages from github by version or sha1
(it's enough to use first 7 characters from SHA1):
1. by sha1
FOO_VERSION = 1234567
FOO_SITE = http://github.com/user/package/tarball/branch

2. by version
FOO_VERSION = v1.0
FOO_SITE = http://github.com/user/package/tarball/$(FOO_VERSION)



Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>