Move to thin manifests

File integrity is already checked by git, so there is no need to store
checksums for files in repository. This also eliminates situations where
ebuild is updated but manifest isn't and package is broken.

http://wiki.gentoo.org/wiki/Repository_format/package/Manifest#Thin_Manifest
Merge pull request #40 from dummyunit/thin-manifests

Move to thin manifests