ctype tweaks

None of these explains the Windows assertion failure.
 end.c - post-3.6.0
 options.c - in #else block of #if win32
 winmenu.c - X11

src/end.c

@@ -1678,7 +1678,7 @@ boolean ask;
                 pfx = !strncmpi(buf, "the ", 3) ? 0
                       : !strncmpi(buf, "an ", 3) ? 1
                         : !strncmpi(buf, "a ", 2) ? 2
-                          : !isdigit(buf[2]) ? 4 : 0;
+                          : !digit(buf[2]) ? 4 : 0;
                 if (class_header)
                     ++pfx;
                 Sprintf(buftoo, "%*s%s", pfx, "", buf);