Upgrade debhelper compatibility level

[broder]

Now that Sarge is gone, we no longer need to declare a debhelper compatibility level of 4. Furthermore, we probably shouldn't, and there are probably places where we're not actually compatible with dh 4.

So long as Etch and Hardy are still around, we can only bump it to 5. But we probably should do so anyway.

[geofft]

I'm not yet sure how straightforward this is. A cursory scanning of the manpages indicates dh_strip --dbg-package changed its semantics after v4, but nothing else at this version, so maybe this will be easy, but we should definitely look more carefully.

[jdreed]

This is actively throwing warnings during the build process these days, so let's go ahead and do this.

[jdreed]

OK, the only things calling dh_strip are debathena/third/schroot (I really think we can move this to the attic, it's jaunty-only, right?) and third/moira, and both are using dh5 syntax anyway, so we can go to 5.

We should probably go to 6, which is available in everything we care about. The major change appears to be the maintainer script fragment reverse order. Is there anything we have that could possibly care about that? I don't thinkso

[jdreed]

r25600, all added as UNRELEASED changes.

[jdreed]

I'm not rebuilding the world yet, we'll pick most of this up in the Qantas rebuild. I reserve the right to flip out and rebuild everything later. Ben notes we might end up not building some of these before going straight to 7 once Hardy is dead, but since this only affects builds, I think I'd prefer a bunch of UNRELEASED packages and attrition to possible skew and the time and effort involved in a full rebuild, particularly at this point in the release cycle.