rebase: --abort doesn't strip away the target changeset (issue2220)
When a changeset is skipped, rebase keeps the previous target as next
target and if the skipped cset is the first one, the recorded target is
actually the original target.
--abort did not detect this situation but simply stripped away the cset.
foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
rev offset length base linkrev nodeid p1 p2
0 0 6 0 0 26d3ca0dfd18 000000000000 000000000000
1 6 7 1 1 d267bddd54f7 26d3ca0dfd18 000000000000