Provide base href in Echo's HTML emails
While working on my own Echo notifications for CategoryWatch, I came
across this bug. I was happy to see that someone else identified this
a while back.
Wikitext-to-html production for the body of Echo messages does
not fully qualify urls. This means that links are created pointing
to, for example, "/w/index.php..." instead of
"http://example.com/w/index.php...". Supplying a base URL in the html
for the message fixes this problem.