cmd_pull didn't support --squash correctly.

We should implement it as
	git fetch ...
	git subtree merge ...

But we were instead just calling
	git pull -s subtree ...

because 'git subtree merge' used to be just an alias for 'git merge -s
subtree', but it no longer is.
diff --git a/git-subtree.sh b/git-subtree.sh
index cccc340..8baa376 100755
--- a/git-subtree.sh
+++ b/git-subtree.sh
Binary files differ