Prefix UPDATE & DROP TABLE IF EXISTS statements in prefix.sh

I've tested the patch and can say it works. Don't know if we need this feature, as neither statement is used by Drupal core.

I would say: go for it. It works, and I already once had to hand-edit all my custom modules because this thing was not in the prefix.sh
This works as expected, and makes prefixing contributed sql files easier.

DROP TABLE IF EXISTS does not work with postgresql (it does not support IF EXISTS statement)

Tested against privatemsg.mysql which has both of these statements and it works as advertised. Thanks!

Er. I suppose I should've actually tested the patch rather than just copy/paste the lines I needed, eh? ;)

Here is a re-rolled version that applies against HEAD.

And here's one for 4.6 as well.

Let's try that again and pretend I don't have a crappy Windows text editor. :P

Sorry, I will quit spamming now. :P

applied