Created new data types Filename' and FontSpec', intended to be

opaque to all platform-independent modules and only handled within
per-platform code. `Filename' is there because the Mac has a magic
way to store filenames (though currently this checkin doesn't
support it!); `FontSpec' is there so that all the auxiliary stuff
such as font height and charset and so on which is needed under
Windows but not Unix can be kept where it belongs, and so that I can
have a hope in hell of dealing with a font chooser in the forthcoming
cross-platform config box code, and best of all it gets the horrid
font height wart out of settings.c and into the Windows code where
it should be.
The Mac part of this checkin is a bunch of random guesses which will
probably not quite compile, but which look roughly right to me.
Sorry if I screwed it up, Ben :-)

[originally from svn r2765]

winmisc.c

@@ -12,3 +12,26 @@ void platform_get_x11_auth(char *display, int *proto,
 {
     /* We don't support this at all under Windows. */
 }
+
+Filename filename_from_str(char *str)
+{
+    Filename ret;
+    strncpy(ret.path, str, sizeof(ret.path));
+    ret.path[sizeof(ret.path)-1] = '\0';
+    return ret;
+}
+
+char *filename_to_str(Filename fn)
+{
+    return fn.path;
+}
+
+int filename_equal(Filename f1, Filename f2)
+{
+    return !strcmp(f1.path, f2.path);
+}
+
+int filename_is_null(Filename fn)
+{
+    return !*fn.path;
+}