helm-mode conflict with ido-everywhere.

Fine, I think helm could be instead of ido.
But, in very less case, ido is better choice, and few package only support ido.

when enable ido-everywhere feature and helm-mode.

``` cl
(require 'ido)
(ido-mode t)
(ido-everywhere 1)

(require 'helm-config)
(helm-mode 1)
```

first time invoke `C-x v d`,  runs helm-mode-vc-dir.
second time invoke `C-x v d`,  use ido instead of helm. 
