Not all cogd options require EUID=0

`cogd -V` and `cogd --show-config` can now be run as normal users (the
latter assuming you have read access to the configuration file...)
Force apt-get to use default / previous configs
Fix cwtool quoting / ordering problems
Properly re-schedule CFM runs

This avoids the 'message repeated 939226825 times: [ Another
configuration management run in progress; skipping.]' lines from
appearing in syslog.
Support diff output for file remediation

The new `difftool' configuration directive lets users specify what
diff they wish to use (so they can increase context, switche to
side-by-side, etc.), but ships with a sane default.

This makes file remediation much easier to troubleshoot.

Updated the vim syntax file to support the new directive.