Don't generate git patches that rename a file to multiple destinations
With this patch, instead of generating N renames, we'll generate
1 rename and N-1 copies.
Ideally the rename should come after the copies instead of before
them, but that'd be harder to do.
% init
% commit
adding base
% qnew mqbase
% qrefresh
% qdiff
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@ base
-base
+patched