improve selectsave handling for Windows

If there were outdated savefiles encountered during
startup, each individual one was getting a wait_synch
that required a <return> even though a message window
wasn't being used at that point.

Allow suppression of the individual per-file wait_synch()
calls on Windows, so that a single one can be done once
the selectsave processing is overwith.

This was a little messy because an indicator had to flow
down through validate(), uptodate(), etc.

There shouldn't be any change in how things behave on
any non-Windows platforms.

src/bones.c

@@ -613,7 +613,7 @@ getbones(void)
         return 0;
     }
 
-    if (validate(nhfp, gb.bones) != 0) {
+    if (validate(nhfp, gb.bones, FALSE) != 0) {
         if (!wizard)
             pline("Discarding unusable bones; no need to panic...");
         ok = FALSE;