Obtain complete version info for LIBRARY and PACKAGE.
LIBRARY is a symbol denoting a named feature, or a library name
as string. PACKAGE is a symbol denoting an ELPA package. If
omitted or nil, default to LIBRARY.
If SHOW is non-nil, show the version in the minibuffer.
When called interactively, prompt for LIBRARY. When called
interactively with prefix argument, prompt for PACKAGE as well.
Return a string with complete version information for LIBRARY.
This version information contains the version from the headers of
LIBRARY, and the version of the installed PACKAGE, the LIBRARY is
part of. If PACKAGE is not installed, or if the PACKAGE version
is the same as the LIBRARY version, do not include a package
version.
(fn LIBRARY &optional PACKAGE SHOW)