Overwrite argv to set process title, eliminating 16-character prctl() limit.

I've modified qemu to overwrite its arguments to set the process title, since its current prctl() method has a 16-character limit.

I posted the original patch to qemu-devel, made the changes others suggested, then re-posted to qemu-devel. I flailed around a bit with the patch submission process and think I finally got it right, but haven't been able to gain the notice of a committer to have this pushed. Maybe this will get more attention when reported in the BTS.