Add lladdend function and use in makewordlist.

Add a new function that adds an object to the end of a linked list.
We make use of this in makewordlist, which means we search for keys
containing words from the start of the email address first, rather than
starting with the words at the end. When you're dealing with TLDs like
com, net, org this makes a big difference, as you don't end up with a
huge list from the first word you try.