fix 'convert' with single commit repositories The attached patch passes the three 'convert' testcases, and also is able to successfully convert the git.git repository.

#!/bin/sh

mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m "test" -d "1000000 0"
hg verify
hg parents
hg status
hg rollback
hg verify
hg parents
hg status