Throw file-error from lread/load.

deuce-loadup.el crashes for me due to
```el
(condition-case nil
    ;; Don't get confused if someone compiled this by mistake.
    (load "loaddefs.el")
  ;; In case loaddefs hasn't been generated yet.
  (file-error (load "ldefs-boot.el")))
```
file-error should be thrown anyways. The first commit is pretty obvious.