convert: refactor sink initialisation, to remove hardcoding of hg
We also introduce options to explicitly set the source and destination
repository types.
Improve testing of corner cases a little.
#!/bin/sh
hg init a
cd a
echo a > a
hg add -n
hg st
hg add
hg st
echo b > b
hg add -n b
hg st
hg add b
hg st
echo % should fail
hg add b
hg st
hg ci -m 0
echo % should fail
hg add a
echo aa > a
hg ci -m 1
hg up 0
echo aaa > a
hg ci -m 2
hg merge
hg st
echo % should fail
hg add a
hg st
hg ci -m merge
echo % issue683
hg rm a
hg st
echo a > a
hg add a
hg st