Disable ido when completion-extra-properties is non-nil

"completion-extra-properties" appears to be a new variable that has
important effects on how completion occurs, and ido doesn't support
it.

This provides a workaround for #8.

ido-ubiquitous.el

@@ -143,6 +143,7 @@ happen, so this feature may simply not work in some cases."
   "Ido-based method for reading from the minibuffer with completion.
    See `completing-read' for the meaning of the arguments."
   (if (or inherit-input-method          ; Can't handle this arg
+          (bound-and-true-p completion-extra-properties) ; Can't handle this
           (not ido-mode)
           (not ido-ubiquitous-mode)
           ;; Avoid infinite recursion from ido calling completing-read