[MaraDNS list] Deadwood updates

Investigating the bug that Domenico Rotondi reported, I discovered
that there have been some issues with RD (recursion desired) being
correctly set when both upstream_servers and root_servers are set.  I
have updated the code and hopefully RD will now always have the
correct value in DNS queries sent upstream.

In addition, I am updating the Deadwood's parser:

* I consider it a bug if any valid dwood3rc file does not parse in
Python 2.  That in mind, I have updated the dwood3rc parser to not
allow parameters to have any leading whitespace (since whitespace is
significant in Python)

* It is no longer allowed to set a given root_servers or
upstream_servers node more than once.  In other words, a configuration
like this will now raise an error:

upstream_servers["example.com."] = "127.0.0.1"
upstream_servers["example.com."] = "10.1.2.3"

or

upstream_servers["example.net."] = "192.168.1.1"
root_servers["example.net."] = "192.168.1.1"

The updated code can be downloaded here:

http://maradns.org/deadwood/snap/

- Sam