Bug#671084: lintian: warn against ~dfsg versions

[Daniel Schepler <dschepler@gmail.com>]

Package: lintian
Version: 2.5.6
Severity: wishlist

I've recently noticed a few instances of packages being assigned
versions of something like 1.2~dfsg-3.  That doesn't make sense: the ~
character is supposed to be for marking pre-release version tags from
upstream like ~beta2, while the "dfsg" tag means it's a repack of the
upstream release to remove non-free files.  The two conflict with each
other.  So it would be nice if Lintian would flag this as a probable
error, and suggest using "1.2+dfsg-3" instead.

According to my quick counts, there are currently 73 source packages
and 238 binary packages (at least for amd64) with such versions in sid
(excluding duplicates due to multiple versions of the same package
having ~dfsg in them).

I also noticed there are a couple source packages with ~repack, which
doesn't make sense for the same reasons, so maybe it could catch those
too.

(I guess this is sort of the flip side of #649277 -- that one deals
with missing ~ where it should probably be used, this one deals with
using ~ where it doesn't make sense.)
-- 
Daniel Schepler