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If there were outdated savefiles encountered during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.

include/extern.h

@@ -939,7 +939,7 @@ extern void paniclog(const char *, const char *);
 extern void testinglog(const char *, const char *, const char *);
 extern int validate_prefix_locations(char *);
 #ifdef SELECTSAVED
-extern char *plname_from_file(const char *);
+extern char *plname_from_file(const char *, boolean);
 #endif
 extern char **get_saved_games(void);
 extern void free_saved_games(char **);
@@ -2421,7 +2421,7 @@ extern int restore_menu(winid);
 #endif
 extern void minit(void);
 extern boolean lookup_id_mapping(unsigned, unsigned *);
-extern int validate(NHFILE *, const char *);
+extern int validate(NHFILE *, const char *, boolean);
 extern void reset_restpref(void);
 extern void set_restpref(const char *);
 extern void set_savepref(const char *);

include/hack.h

@@ -830,6 +830,7 @@ typedef struct {
 #define UTD_CHECKFIELDCOUNTS           0x02
 #define UTD_SKIP_SANITY1               0x04
 #define UTD_SKIP_SAVEFILEINFO          0x08
+#define UTD_WITHOUT_WAITSYNCH_PERFILE  0x10
 
 #define ENTITIES 2
 struct valuable_data {