bug#15236: 24.3.50; Save file with Unicode chars in name on MS Windows replaces chars by SPCs

[Drew Adams <drew.adams@oracle.com>]

This might be a duplicate of #7100 and #12807 - I cannot tell.  In any
case, the recipe here is different.

Whether the same bug or not, it seems like this kind of bug should be a
priority in 2013, not relegated to the wishlist since 2010.  Is it
possible that Emacs on MS Windows still cannot save files with Unicode
chars in the name?  Am I missing something?  Is this a Windows
limitation in general, perhaps?

emacs -Q

Create a new file buffer with a Unicode character, such as GREEK SMALL
LETTER LAMBDA, in the file name.  Note that the mode line of the buffer
shows the file name (buffer name) correctly, i.e., with the lambda chars.

Enter some text in the file buffer, including, for example, such a char.
Set the encoding to utf-8, to be sure.  Save the file.  The mode line
still shows the file name correctly.  All seems OK.  No error from Emacs.

But the name of the file actually created has a SPC char in place of
each GREEK SMALL LETTER LAMBDA char that should be there.  You can see
this in Dired, and if you open the file from there you can see it in the
mode line or via M-: (buffer-file-name).

Can this be fixed?  If not, how about letting the user know when s?he
saves the file that Emacs (or Windows?) has in fact changed the name?

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-23 on ODIEONE
Bzr revision: 113986 rgm@gnu.org-20130823185841-zoy6h1qk433ibrlf
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'