Snapper client: print features compiled in

Convenient to see what features have been compiled into the client tool,
sample output:

$ snapper --version
snapper 0.2.3 (btrfs,ext4,lvm,no-zypp,no-xattr,rollback,btrfs-quota,no-pam)

match the --enable- parameters for configure.
This should be HAVE_PAM.