Comment 2 for bug 1079723

I think i came up with a compromise which leaves the existing conf files as-is and won't add any new syntax.

Let's take the example
        usercmd = ['env', 'FLAGFILE=A', 'NETWORK_ID=foobar', 'dnsmasq', 'foo']
        f = filters.DnsmasqFilter("/usr/bin/dnsmasq", "root")

we will look for "/usr/bin/dnsmasq", if it does not exist then we look for

"/bin/dnsmasq"
"/sbin/dnsmasq"
"/usr/sbin/dnsmasq"

If none exists, we just return the original path "/usr/bin/dnsmasq" so the command will fail just as it would have before this patch.