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
hg init
echo a > a
hg commit -A -ma
echo a >> a
hg commit -mb
echo a >> a
hg commit -mc
hg up 1
echo a >> a
hg commit -md
hg up 1
echo a >> a
hg commit -me
hg up 1
echo % should fail because not at a head
hg merge
hg up
echo % should fail because \> 2 heads
hg merge
echo % should succeed
hg merge 2
hg commit -mm1
echo % should succeed - 2 heads
hg merge
hg commit -mm2
echo % should fail because 1 head
hg merge
true