Fix a minor problem in identifying squashes vs. normal splits.

This didn't seem to have any noticeable side effects other than
suspicious-looking log messages when you used -d.
diff --git a/git-subtree.sh b/git-subtree.sh
index 0949fef..cccc340 100755
--- a/git-subtree.sh
+++ b/git-subtree.sh
Binary files differ