fix crash when SetCandidateRelease is used

apt-pkg/depcache.cc

@@ -1522,7 +1522,7 @@ bool pkgDepCache::SetCandidateRelease(pkgCache::VerIterator TargetVer,
 	 if (itsFine == false)
 	 {
 	    // change the candidate
-	    Changed.push_back(make_pair(oldCand, TargetVer));
+	    Changed.push_back(make_pair(V, TargetVer));
 	    if (SetCandidateRelease(V, TargetRel, Changed) == false)
 	    {
 	       if (stillOr == false)

apt-private/private-install.h

@@ -95,6 +95,9 @@ struct TryToInstall {
 	 Cache->GetDepCache()->SetCandidateVersion(s->first);
 
       bool Success = true;
+      // the Changed list contains:
+      //   first: "new version" 
+      //   second: "what-caused the change" 
       std::list<std::pair<pkgCache::VerIterator, pkgCache::VerIterator> > Changed;
       for (std::list<std::pair<pkgCache::VerIterator, std::string> >::const_iterator s = start.begin();
 		s != start.end(); ++s)

test/integration/test-bug-709560-set-candidate-release

@@ -0,0 +1,36 @@
+#!/bin/sh
+set -e
+
+TESTDIR=$(readlink -f $(dirname $0))
+. $TESTDIR/framework
+setupenvironment
+configarchitecture 'amd64'
+
+insertpackage 'experimental' 'foo' 'all' '2.0' 'Depends: foo-dep (= 2.1)'
+insertpackage 'experimental' 'foo-dep' 'all' '2.1'
+
+
+(
+cat <<EOF
+Package: *
+Pin: release a=experimental
+Pin-Priority: -10
+EOF
+) > rootdir/etc/apt/preferences
+
+
+setupaptarchive
+
+testequal "Reading package lists...
+Building dependency tree...
+Selected version '2.0' (experimental [all]) for 'foo'
+Selected version '2.1' (experimental [all]) for 'foo-dep' because of 'foo'
+The following extra packages will be installed:
+  foo-dep
+The following NEW packages will be installed:
+  foo foo-dep
+0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
+Inst foo-dep (2.1 experimental [all])
+Inst foo (2.0 experimental [all])
+Conf foo-dep (2.1 experimental [all])
+Conf foo (2.0 experimental [all])" aptget install -q0 -s foo/experimental