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
# http://www.selenic.com/mercurial/bts/issue352
hg init foo
cd foo
A=`printf 'he\rllo'`
echo foo > "$A"
hg add
hg ci -A -m m
rm "$A"
echo foo > "hell
o"
hg add
hg ci -A -m m
echo foo > "$A"
hg debugwalk
exit 0