bug#6652: bug#6679: locate-library does not provide a default when called interactively

[Eli Zaretskii]

> From: Štěpán Němec
>  <stepnem@gmail.com>
> Date: Sat, 28 Mar 2020 22:59:44 +0100
> Cc: 6679@debbugs.gnu.org
> 
> On Tue, 20 Jul 2010 21:14:09 -0600
> Kevin Rodgers wrote:
> 
> > Assuming that complexity is justified, it ought to be factored into a
> > read-library-name utility that both find-library and locate-library use.
> 
> The first part has since happened (`read-library-name'), all that is
> needed is the latter. Patch attached.
> 
> > `C-h a -library\'' returns apropos-library and load-library in addition to
> > find-library and locate-library, but it's not clear to me that they would
> > benefit from a default.
> 
> The patch also handles `load-library'. The set of arguments/completions
> expected/provided by `apropos-library' is slightly different and
> requires other validation, so `read-library-name' wouldn't really help
> there.

Thanks, pushed to the master branch.