do not require non-broken systems in 'upgrade'

There is a good chance that the attempt will fail, but if a user
mentions certain packages explicitly on the commandline there is a
chance that this will consist of a broken system which is resolved
by upgrading more packages then just the mentioned.

This limitation was not effecting external resolvers.

apt-pkg/upgrade.cc

@@ -136,12 +136,8 @@ static bool pkgAllUpgradeNoNewPackages(pkgDepCache &Cache, OpProgress * const Pr
       Progress->OverallProgress(0, 100, 1, _("Calculating upgrade"));
 
    pkgDepCache::ActionGroup group(Cache);
-
    pkgProblemResolver Fix(&Cache);
 
-   if (Cache.BrokenCount() != 0)
-      return false;
-   
    // Upgrade all installed packages
    for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; ++I)
    {
@@ -182,12 +178,8 @@ static bool pkgAllUpgradeWithNewPackages(pkgDepCache &Cache, OpProgress * const
       Progress->OverallProgress(0, 100, 1, _("Calculating upgrade"));
 
    pkgDepCache::ActionGroup group(Cache);
-
    pkgProblemResolver Fix(&Cache);
 
-   if (Cache.BrokenCount() != 0)
-      return false;
-
    // provide the initial set of stuff we want to upgrade by marking
    // all upgradable packages for upgrade
    for (pkgCache::PkgIterator I = Cache.PkgBegin(); I.end() == false; ++I)