diff-tree: show hex sha1 of the single-commit argument case correctly.
diff-tree: show hex sha1 of the single-commit argument case correctly.

We can't just do the "sha1_to_hex()" thing directly, since the
buffer in question will be overwritten by the name of the parent.

So teach diff_tree_commit() to generate the proper hex name itself.

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git