Fix weather applet preferences find function

If you type "Barcelona" into the find entry then it will take you to
Barcelona, Venezuela.  Clicking "Find Next" doesn't jump to the next
entry (the one in Spain), however.

The problem is the code only looks at the direct parent of the first
match when searching for the second match.  Since there aren't any
more countries in Central America after Venezuela the search stops.

This commit recursively searches all ancestors for matches.

See bug 424639 for more details.