declare-function file names

[Richard Stallman <rms@gnu.org>]

I just saw this

    +(declare-function dos-8+3-filename "../dos-fns.el" (filename))

and realized that we never discussed precisely what these file name
arguments would mean.  In particular we never discussed how directories
would be handled.

Since Lisp library names must be unique even between directories, I
think that we should not include directory names in this argument.
check-declare should ignore any directory name if specified.