py3: call branchmap.items() on py3 and continue to call iteritems() on py2
Mercurial's source transformer also replaces the 'def iteritems(' in
branchmap by 'def items(', so we need to call whichever version is
there.
Test that share-clones use the cache in the original repository.
$ . $TESTDIR/testlib/common.sh
$ hg init share-base
$ cd share-base/
$ cat >> .hg/hgrc <<EOF
> [extensions]
> evolve=
> share=
> EOF
$ hg debugbuilddag .+3:branchpoint+4*branchpoint+2
$ cd ..
$ hg --config extensions.share= share -U share-base share-client
$ cd share-client
$ hg debugupdatecache
$ test -d .hg/cache
[1]
$ test -d ../share-base/.hg/cache