Merge branch 'jc/maint-1.7.3-checkout-describe'

* jc/maint-1.7.3-checkout-describe:
  checkout -b <name>: correctly detect existing branch

builtin/checkout.c

@@ -1072,7 +1072,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		if (strbuf_check_branch_ref(&buf, opts.new_branch))
 			die(_("git checkout: we do not like '%s' as a branch name."),
 			    opts.new_branch);
-		if (!get_sha1(buf.buf, rev)) {
+		if (ref_exists(buf.buf)) {
 			opts.branch_exists = 1;
 			if (!opts.new_branch_force)
 				die(_("git checkout: branch %s already exists"),