[RFC] explicitly allow setuid and setgid permissions in templates

There are no checks for setuid and setgid permissions right now which could potentially be a security risk.

a) setugid=yes allows both setuid and setgid permissions in all files in the package
b) setugid="usr/bin/su" per-file rules

split setuid and setgid rules
c) setuid=yes; setgid=yes
d) setuid="usr/bin/su"; setgid=""

I will prepare a post-install hook when it's decided which method is preferred. I like c) the most, because there are some packages providing just setgid binaries without needing setuid (mlocate). b) and d) sound too verbose to me and if a package provides a set{u,g}id binary, the whole package is trusted.

I would also like to ask someone with access to the binary repository to post here which packages have set{u,g}id binaries.

cc @ericonr