bug#15159: 24.3.50; doc of `file-relative-name'

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 21 Aug 2013 20:42:19 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> The doc says nothing about whether arg FILENAME needs to be absolute or
> relative, and in fact it can be either.  It is clear enough what the
> function does if it is absolute, but the doc should say explicitly what
> it does for a relative FILENAME, namely, it expands the FILENAME in the
> `default-directory' of the current buffer.

Sorry, but I see nothing unclear in this doc string:

  (file-relative-name FILENAME &optional DIRECTORY)

  Convert FILENAME to be relative to DIRECTORY (default: `default-directory').
  This function returns a relative file name which is equivalent to FILENAME
  when used with that default directory as the default.

"Convert FILENAME to be relative to DIRECTORY" is accurate and
unequivocal.  The fact that relative file names are treated as
relative to the current buffer's default-directory is what Emacs does
with _every_ file name in _any_ function; if users don't know this
basic fact, they will have problems all over the place.