Allow multi-file select on Win9x as well

The patch supplied is for tk/win/tkWinDialog.c

With 8.4, the ability to select multiple files via
the tk_getOpenFile was supposed to be allowed. I downloaded
the latest sources and noticed that this was indeed
done for WinNT but not for Win9x. As far as I can tell,
the very EXACT changes also apply to the Win9x platform.

So, I copied the logic from the WinNT side to the Win9x side
and (made small changes to allow regular TCHAR strings).

Since we are now allowing multiple files, I also increased
the buffer size to be twice as big as MAX_PATH.

I also noticed that in the Win9x side, we save and restore
the current-working directory whereas on WinNT we do not.
I do not know the reason for this (and I do not have
access to a WinNT machine to see why). I did not modify this
part since there may have been a good reason why the current
working directory does not have to be saved and restored.

I personally recommend doing the same thing for both platforms
so that the code for the two is as similar as possible.

Regards,
Haneef