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.
adding start
adding new
% new file
diff --git a/new b/new
new file mode 100644
--- /dev/null
+++ b/new
@@ -0,0 +1,1 @@
+new
% copy
diff --git a/new b/copy
copy from new
copy to copy
% rename
diff --git a/copy b/rename
rename from copy
rename to rename
% delete
diff --git a/rename b/rename
deleted file mode 100644
--- a/rename
+++ /dev/null
@@ -1,1 +0,0 @@
-new
adding src
% chmod 644
diff --git a/src b/src
old mode 100644
new mode 100755
% rename+mod+chmod
diff --git a/src b/dst
old mode 100755
new mode 100644
rename from src
rename to dst
--- a/dst
+++ b/dst
@@ -3,3 +3,4 @@ 3
3
4
5
+a
% nonexistent in tip+chmod
diff --git a/src b/src
old mode 100644
new mode 100755