Log Message:
Make bbdb build with emacs-24.

Without this patch, build fails with the following error:

 bbdb-mhe.el:56:1:Error: Invalid function: ...

Emacs is partially responsible for this, but the upstream won't fix it
since the cause of this (old-style backquote) will be removed in
emacs-25.

Patch provided by Makoto Fujiwara in PR 44963.