cfengine: using /var/cfengine instead of /var/lib/cfengine (and other changes)

- using /var/cfengine instead of /var/lib/cfengine 
- creating symlins in /var/cfengine/bin
- auto-detecting optional dependencies during build
- adding 'acl' to list of optional dependencies
with those modifications I was able to run "cf-agent --bootstrap <policy-server>" immediately after install, and client happily joined our CFEngine controller network (cfengine master is running on Debian server).