Revert "Allow empty-string-as-default compatibility mode in more cases"

Fixes #17. Breaks #16 again, but that can't be helped.

This reverts commit f327ce03e948965b1f66f8c3cdb7f429fa416c38.

ido-ubiquitous.el

@@ -271,6 +271,7 @@ This behavior is disabled by setting
 `ido-ubiquitous-enable-compatibility' to nil."
   (if (and ido-ubiquitous-enable-compatibility
            (eq ido-cur-item 'list)
+           ido-require-match
            (null ido-default-item)
            (not current-prefix-arg)
            (string= ido-text "")