obslog: don't overwrite {rev} keyword from changeset context
Now that we have the whole changeset in the formatter context, there's
no need to explicitly add {rev}.
We should also deprecate the {shortdescription} keyword since it's no
longer needed, but I don't know how to do that.
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