Get the original version of the library defining FUNCTION.
The original version is stored in the X-Original-Version header.
This header is added by the MELPA package archive to preserve
upstream version numbers.
If SHOW is non-nil, show the version in mini-buffer.
This function is mainly intended to find the version of a major
or minor mode, i.e.
(pkg-info-defining-library-version 'flycheck-mode)
Return the version of the library defining FUNCTION. Signal an
error if FUNCTION is not a valid function, if its defining
library was not found, or if the library had no proper version
header.
(fn FUNCTION &optional SHOW)