Improve debian Release file creation

* add Suite/Codename (projid) to Release (should be useful for pinning, also aptitude can show Suite with %t in aptitude::UI::Package-Display-Format)
* add SHA1+SHA256 checksums (only MD5 until now?...) (The Field for MD5 is named "MD5Sum", the fields for the SHA checksums are "SHA1" and "SHA256", see ftp://ftp.debian.org/debian/dists/wheezy/Release)
* don't add checksum of the partial Release file itself (kinda useless)

I didn't test it (I only checked a colon ":" in Suite label was working with aptitude).