tests/test-merge3

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
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
touch b
hg add b
rm b
hg commit -A -m"comment #1" -d "1000000 0"