Fixed my sbuild patch

I just revisited the sbuild patch to support autobuilding experimental with build-deps from experimental that I did some months back. It should work now.

I didn't actually check whether it does yet, but then the changes I just made involve just four lines. Or so.

Call me lazy.

It's installed on quickstep now, my m68k mac that's Debian's only m68k buildd for the experimental distribution (and which is keeping up nicely). If it doesn't give us any problems in the next (few) week(s), I'm sure there'll be much rejoicing.