Adding auto-highlite code. This might be a bit contentious, but it seemed to get...

Adding auto-highlite code.  This might be a bit contentious, but it seemed to get good response on the DEVEL list, so trying it out.  Things to note: the clicked color isn't the best, but we can also remove that and ONLY have mouseover coloring if we can't find a better color.  The JavaScript was mostly swiped from phpMyAdmin, and it is fairly well written and fairly mature; I don't think there will be widespread problems with it.  That said, this is a pretty big leap for SquirrelMail.  We might want to have this be a user-configurable option instead of making it default when javascript_on is active.  Unfortunately, doing it as a plugin is pretty much out of the question.  Let's see how it goes.  If things go really well, I'd like to port this to STABLE, since this stuff probably won't even see the light of day if we get templating in to 1.5.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@9016 7612ce4b-ef26-0410-bec9-ea0150e637f0