bookmarks: fix head selection for merge with two bookmarked heads
A type mismatch caused the search for the other head to fail. The code is
fragile, and instead it ended up using the 'first' bookmark head, but the
ordering is undefined and it could thus randomly use the wrong bookmarkhead
and fail with:
$ hg up -q -C e@diverged
$ hg merge
abort: merging with a working directory ancestor has no effect
$ hg init rep
$ cd rep
$ mkdir dir
$ touch foo dir/bar
$ hg -v addremove
adding dir/bar
adding foo
$ hg -v commit -m "add 1"
dir/bar
foo
committed changeset 0:6f7f953567a2
$ cd dir/
$ touch ../foo_2 bar_2
$ hg -v addremove
adding dir/bar_2
adding foo_2
$ hg -v commit -m "add 2"
dir/bar_2
foo_2
committed changeset 1:e65414bf35c5
$ cd ../..
$ hg init sim
$ cd sim
$ echo a > a
$ echo a >> a
$ echo a >> a
$ echo c > c
$ hg commit -Ama
adding a
adding c
$ mv a b
$ rm c
$ echo d > d
$ hg addremove -n -s 50 # issue 1696
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)
$ hg addremove -s 50
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)
$ hg commit -mb
$ cd ..