Add core copy detection algorithm
This adds findcopies, which detects merge-relevant copies between
files in a pair of manifests back to the merge ancestor.
While the merge code invokes the copy detection routine, it does not
yet use the result.
#!/bin/sh
hg init
touch unknown
touch a
hg add a
hg ci -m "1" -d "1000000 0"
touch b
hg add b
hg ci -m "2" -d "1000000 0"
echo %% Should show unknown
hg status
hg revert -r 0 --all
echo %% Should show unknown and b removed
hg status
echo %% Should show a and unknown
ls