Fix default clone destination
The default clone wasn't working:
$ hg clone hg
abort: repository hg/.hg not found!
This was because we were creating the destination directory from the
default, then checking whether it existed to determine whether to
expand the path.
1:3aa14bbc23d9
0:8633637036c1
3aa14bbc23d9 tip
8633637036c1
8633637036c1+
8633637036c1
3aa14bbc23d9 tip
merging file1
3aa14bbc23d9 tip
3aa14bbc23d9 tip
3aa14bbc23d9 tip
3aa14bbc23d9 tip