bug#21821: 25.0.50; invalid byte code in dired-x.elc

[Daniel McClanahan]

Byte-compiling lisp/dired-x.el generates invalid byte code in
dired-x.elc, which manifests when attempting to use dired-x functions.
Typically I resolve this by opening and manually evaluating
dired-x.el.

To reproduce on emacs -Q built from master:
1. Byte-recompile dired-x.el
2. Open dired-x.elc.
3. Attempt to evaluate the buffer. It should fail at the attempted
evaluation of `dired-x-bind-find-file' with an "invalid byte code"
error.