tests/test-issue1306

allow clone into existing but empty directories

echo % initialize remote repo with branches
hg init remote
cd remote
echo a > a
hg ci -Ama
hg branch br
hg ci -Amb
echo c > c
hg ci -Amc
hg log

cd ..
echo % try cloning -r branch
hg clone -rbr remote local1
hg -R local1 parents

echo % try cloning -rother clone#branch
hg clone -r0 remote#br local2
hg -R local2 parents

echo % try cloning -r1 clone#branch
hg clone -r1 remote#br local3
hg -R local3 parents