some coordxy and other conversion warnings

When dist2() got changed to use coordxy parameters, a macro that uses
it in its definition was overlooked and it had (int) casts in it.
That caused a warning about possible data loss when the int
then got converted to coordxy for the dist2() call.

Give online2() coordxy parameters instead of int, like its bretheren.

Avoid a couple of implicit conversion warnings where ints were being assigned
to smaller uchar or ints being assigned to smaller short.

A couple of signed vs unsigned warnings on some rumor processing.

Avoid some signed vs unsigned warnings in mdlib/makedefs where a signed int
param eventually got used in an external call that took size_t.
Eliminate all of it by just having the outer NetHack routine also take
a size_t.

Lastly, insert some default C99 alternative time-related code
in mdlib/makedefs since asctime() and ctime() are being flagged as
deprecated in the upcoming C23 standard and will now start to trigger
warnings for anyone using a C23-compliant compiler.

sys/msdos/tile2bin.c

@@ -190,7 +190,12 @@ main(int argc, char *argv[])
 #endif
 
     strncpy(tibheader.ident, "NetHack 3.7 MSDOS Port binary tile file", 80);
+#if !defined(NOSTRFTIME)
+    if (!strftime(tibheader.timestamp,
+                  sizeof tibheader.timestamp, "%c", newtime))
+#else
     strncpy(tibheader.timestamp, asctime(newtime), 24);
+#endif
     tibheader.timestamp[25] = '\0';
     tibheader.tilecount = tilecount;
     tibheader.numcolors = num_colors;