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
# a test for issue586

hg init a
cd a
echo a > a
hg ci -Ama

hg init ../b
cd ../b
echo b > b
hg ci -Amb

hg pull -f ../a
hg merge
hg rm -f a
hg ci -Amc

hg st -A